refactor(docs): move from reST to Markdown (#31)

Convert docs from reStructuredText to Markdown so that the changelog
file is compatible with Release Please.

AUTHORS.md

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+# Authors
+
+This example is based on the [original open data analysis](http://opendata.cern.ch/record/5500) by Jomhari, Nur Zulaiha; Geiser, Achim;
+Bin Anuar, Afiq Aizuddin, "Higgs-to-four-lepton analysis example using 2011-2012
+data", CERN Open Data Portal, 2017. DOI: [10.7483/OPENDATA.CMS.JKB8.RR42](https://doi.org/10.7483/OPENDATA.CMS.JKB8.RR42)
+
+The list of contributors in alphabetical order:
+
+- [Audrius Mecionis](https://orcid.org/0000-0002-3759-1663)
+- [Clemens Lange](https://orcid.org/0000-0002-3632-3157)
+- [Daniel Prelipcean](https://orcid.org/0000-0002-4855-194X)
+- [Diyaselis Delgado Lopez](https://orcid.org/0000-0001-9643-9322)
+- [Giuseppe Steduto](https://orcid.org/0009-0002-1258-8553)
+- [Kati Lassila-Perini](https://orcid.org/0000-0002-5502-1795)
+- [Marco Donadoni](https://orcid.org/0000-0003-2922-5505)
+- [Maria Fernando](https://github.com/MMFernando)
+- [Tibor Simko](https://orcid.org/0000-0001-7202-5803)
+- [Vladyslav Moisieienkov](https://orcid.org/0000-0001-9717-0775)

README.md

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+# REANA example - CMS Higgs-to-four-leptons
+
+[![image](https://github.com/reanahub/reana-demo-cms-h4l/workflows/CI/badge.svg)](https://github.com/reanahub/reana-demo-cms-h4l/actions)
+[![image](https://img.shields.io/badge/discourse-forum-blue.svg)](https://forum.reana.io)
+[![image](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/reanahub/reana-demo-cms-h4l/blob/master/LICENSE)
+[![image](https://www.reana.io/static/img/badges/launch-on-reana-at-cern.svg)](https://reana.cern.ch/launch?url=https%3A%2F%2Fgithub.com%2Freanahub%2Freana-demo-cms-h4l&name=reana-demo-cms-h4l&specification=reana.yaml)
+
+## About
+
+This [REANA](http://www.reana.io/) reproducible analysis example studies the
+Higgs-to-four-lepton decay channel that led to the Higgs boson experimental discovery in
+2012\. The example uses CMS open data released in 2011 and 2012. "This research level
+example is a strongly simplified reimplementation of parts of the original CMS Higgs to
+four lepton analysis published in Phys.Lett. B716 (2012) 30-61, arXiv:1207.7235." (See
+Ref. [1](http://opendata.cern.ch/record/5500)).
+
+## Analysis structure
+
+Making a research data analysis reproducible basically means to provide "runnable
+recipes" addressing (1) where is the input data, (2) what software was used to analyse
+the data, (3) which computing environments were used to run the software and (4) which
+computational workflow steps were taken to run the analysis. This will permit to
+instantiate the analysis on the computational cloud and run the analysis to obtain (5)
+output results.
+
+### 1. Input data
+
+The analysis takes the following inputs:
+
+- the list of CMS validated runs included in the `data` directory:
+  - `Cert_190456-208686_8TeV_22Jan2013ReReco_Collisions12_JSON.txt`
+- a set of data files in the [ROOT](https://root.cern.ch/) format, processed from CMS
+  public datasets, included in the `data` directory:
+  - `DoubleE11.root`
+  - `DoubleE12.root`
+  - `DoubleMu11.root`
+  - `DoubleMu12.root`
+  - `DY1011.root`
+  - `DY1012.root`
+  - `DY101Jets12.root`
+  - `DY50Mag12.root`
+  - `DY50TuneZ11.root`
+  - `DY50TuneZ12.root`
+  - `DYTo2mu12.root`
+  - `HZZ11.root`
+  - `HZZ12.root`
+  - `TTBar11.root`
+  - `TTBar12.root`
+  - `TTJets11.root`
+  - `TTJets12.root`
+  - `ZZ2mu2e11.root`
+  - `ZZ2mu2e12.root`
+  - `ZZ4e11.root`
+  - `ZZ4e12.root`
+  - `ZZ4mu11.root`
+  - `ZZ4mu12.root`
+- CMS collision data from 2011 and 2012 accessed "live" during analysis via
+  [CERN Open Data](http://opendata.cern.ch/) portal:
+  - [/DoubleMuParked/Run2012C-22Jan2013-v1/AOD](http://opendata.cern.ch/record/6030)
+- CMS simulated data from 2011 and 2012 accessed "live" during analysis via
+  [CERN Open Data](http://opendata.cern.ch/) portal:
+  - [/SMHiggsToZZTo4L_M-125_8TeV-powheg15-JHUgenV3-pythia6/Summer12_DR53X-PU_S10_START53_V19-v1/AODSIM](http://opendata.cern.ch/record/9356)
+
+"The example uses legacy versions of the original CMS data sets in the CMS AOD, which
+slightly differ from the ones used for the publication due to improved calibrations. It
+also uses legacy versions of the corresponding Monte Carlo simulations, which are again
+close to, but not identical to, the ones in the original publication. These legacy data
+and MC sets listed below were used in practice, exactly as they are, in many later CMS
+publications.
+
+Since according to the CMS Open Data policy the fraction of data which are public (and
+used here) is only 50% of the available LHC Run I samples, the statistical significance
+is reduced with respect to what can be achieved with the full dataset. However, the
+original paper Phys.Lett. B716 (2012) 30-61, arXiv:1207.7235, was also obtained with only
+part of the Run I statistics, roughly equivalent to the luminosity of the public sets,
+but with only partial statistical overlap."(See Ref.
+[1](http://opendata.cern.ch/record/5500)).
+
+### 2. Analysis code
+
+The analysis will consist of three stages. In the first stage, we shall build the
+analysis code plugin for the [CMSSW](http://cms-sw.github.io/) analysis framework,
+contained in the `HiggsDemoAnalyzer` directory, using
+[SCRAM](https://twiki.cern.ch/twiki/bin/view/CMSPublic/SWGuideScram), the official CMS
+software build and management tool. In the second stage, we shall process the original
+collision data (using
+[demoanalyzer_cfg_level3data.py](https://github.com/reanahub/reana-demo-cms-h4l/blob/master/code/HiggsExample20112012/Level3/demoanalyzer_cfg_level3data.py)
+) and simulated data (using
+[demoanalyzer_cfg_level3MC.py](https://github.com/reanahub/reana-demo-cms-h4l/blob/master/code/HiggsExample20112012/Level3/demoanalyzer_cfg_level3MC.py)
+) for one Higgs signal candidate with with reduced statistics. In the third and final
+stage, we shall plot the results (using
+[M4Lnormdatall_lvl3.cc](https://github.com/reanahub/reana-demo-cms-h4l/blob/master/code/HiggsExample20112012/Level3/M4Lnormdatall_lvl3.cc)).
+
+"The provided analysis code recodes the spirit of the original analysis and recodes many
+of the original cuts on original data objects, but does not provide the original analysis
+code itself. Also, for the sake of simplicity, it skips some of the more advanced
+analysis methods of the original paper. Nevertheless, it provides a qualitative insight
+about how the original result was obtained. In addition to the documented core results,
+the resulting root files also contain many undocumented plots which grew as a side
+product from setting up this example and earlier examples. The significance of the Higgs
+'excess' is about 2 standard deviations in this example, while it was 3.2 standard
+deviations in this channel alone in the original publication. The difference is
+attributed to the less sophisticated background suppression. In more recent (not yet
+public) CMS data sets with higher statistics the signal is observed in a preliminary
+analysis with more than 5 standard deviations in this channel alone CMS-PAS-HIG-16-041.
+
+The analysis strategy is the following: Get the 4mu and 2mu2e final states from the
+DoubleMuParked datasets and the 4e final state from the DoubleElectron dataset. This
+avoids double counting due to trigger overlaps. All MC contributions except top use
+data-driven normalization: The DY (Z/gamma^\*) contribution is scaled to the Z peak. The
+ZZ contribution is scaled to describe the data in the independent mass range 180-600 GeV.
+The Higgs contribution is scaled to describe the data in the signal region. The (very
+small) top contribution remains scaled to the MC generator cross section." (See Ref.
+[1](http://opendata.cern.ch/record/5500)).
+
+### 3. Compute environment
+
+In order to be able to rerun the analysis even several years in the future, we need to
+"encapsulate the current compute environment", for example to freeze the software package
+versions our analysis is using. We shall achieve this by preparing a
+[Docker](https://www.docker.com/) container image for our analysis steps.
+
+This analysis example runs within the [CMSSW](http://cms-sw.github.io/) analysis
+framework that was packaged for Docker in
+[docker.io/cmsopendata/cmssw_5_3_32](https://hub.docker.com/r/cmsopendata/cmssw_5_3_32/).
+
+### 4. Analysis workflow
+
+The analysis workflow is simple and consists of three above-mentioned stages:
+
+```console
+                           START
+                             |
+                             |
+                             V
+               +-------------------------+
+               |           SCRAM         |
+               +-------------------------+
+                          /     \
+                         /       \
+                        /         \
++-------------------------+     +------------------------+
+| process collision data  |     | process simulated data |
++-------------------------+     +------------------------+
+                \                       /
+                 \ Higgs4L1file.root   / DoubleMuParked2012C_10000_Higgs.root
+                  \                   /
+               +-------------------------+
+               |    produce final plot   |
+               +-------------------------+
+                          |
+                          | mass4l_combine_userlvl3.pdf
+                          V
+                         STOP
+```
+
+The steps processing collision data and simulated data can be run in parallel. We shall
+use the [Snakemake](https://snakemake.readthedocs.io/en/stable/) workflow specification
+to express the computational workflow by means of the following Snakefile:
+
+```python
+rule all:
+    input:
+        "results/mass4l_combine_userlvl3.pdf"
+
+rule scram:
+    input:
+        config["data"],
+        config["code"]
+    output:
+        touch("results/scramdone.txt")
+    container:
+        "docker://docker.io/cmsopendata/cmssw_5_3_32"
+    shell:
+        "source /opt/cms/cmsset_default.sh "
+        "&& scramv1 project CMSSW CMSSW_5_3_32 "
+        "&& cd CMSSW_5_3_32/src "
+        "&& eval `scramv1 runtime -sh` "
+        "&& cp -r ../../code/HiggsExample20112012 . "
+        "&& cd HiggsExample20112012/HiggsDemoAnalyzer "
+        "&& scram b "
+        "&& cd ../Level3 "
+        "&& mkdir -p ../../../../results "
+
+rule analyze_data:
+    input:
+        config["data"],
+        config["code"],
+        "results/scramdone.txt"
+    output:
+        "results/DoubleMuParked2012C_10000_Higgs.root"
+    container:
+        "docker://docker.io/cmsopendata/cmssw_5_3_32"
+    shell:
+        "source /opt/cms/cmsset_default.sh "
+        "&& cd CMSSW_5_3_32/src "
+        "&& eval `scramv1 runtime -sh` "
+        "&& cd HiggsExample20112012/HiggsDemoAnalyzer "
+        "&& cd ../Level3 "
+        "&& cmsRun demoanalyzer_cfg_level3data.py"
+
+rule analyze_mc:
+    input:
+        config["data"],
+        config["code"],
+        "results/scramdone.txt"
+    output:
+        "results/Higgs4L1file.root"
+    container:
+        "docker://docker.io/cmsopendata/cmssw_5_3_32"
+    shell:
+        "source /opt/cms/cmsset_default.sh "
+        "&& cd CMSSW_5_3_32/src "
+        "&& eval `scramv1 runtime -sh` "
+        "&& cd HiggsExample20112012/HiggsDemoAnalyzer "
+        "&& cd ../Level3 "
+        "&& cmsRun demoanalyzer_cfg_level3MC.py"
+
+rule make_plot:
+    input:
+        config["data"],
+        config["code"],
+        "results/DoubleMuParked2012C_10000_Higgs.root",
+        "results/Higgs4L1file.root"
+    output:
+        "results/mass4l_combine_userlvl3.pdf"
+    container:
+        "docker://docker.io/cmsopendata/cmssw_5_3_32"
+    shell:
+        "source /opt/cms/cmsset_default.sh "
+        "&& cd CMSSW_5_3_32/src "
+        "&& eval `scramv1 runtime -sh` "
+        "&& cd HiggsExample20112012/HiggsDemoAnalyzer "
+        "&& cd ../Level3 "
+        "&& root -b -l -q ./M4Lnormdatall_lvl3.cc"
+```
+
+### 5. Output results
+
+The example produces a plot showing the now legendary Higgs signal:
+
+![](https://raw.githubusercontent.com/reanahub/reana-demo-cms-h4l/master/docs/mass4l_combine_userlvl3.png)
+
+The published reference plot which is being approximated in this example is
+<https://inspirehep.net/record/1124338/files/H4l_mass_3.png>. Other Higgs final states
+(e.g. Higgs to two photons), which were also part of the same CMS paper and strongly
+contributed to the Higgs boson discovery, are not covered by this example.
+
+## Running the example on REANA cloud
+
+There are two ways to execute this analysis example on REANA.
+
+If you would like to simply launch this analysis example on the REANA instance at CERN
+and inspect its results using the web interface, please click on the following badge:
+
+[![image](https://www.reana.io/static/img/badges/launch-on-reana-at-cern.svg)](https://reana.cern.ch/launch?url=https%3A%2F%2Fgithub.com%2Freanahub%2Freana-demo-cms-h4l&name=reana-demo-cms-h4l&specification=reana.yaml)
+
+If you would like a step-by-step guide on how to use the REANA command-line client to
+launch this analysis example, please read on.
+
+We start by creating a [reana.yaml](reana.yaml) file describing the above analysis
+structure with its inputs, code, runtime environment, computational workflow steps and
+expected outputs. In this example we are using the Snakemake workflow specification,
+which you can find in the [workflow](workflow) directory.
+
+```yaml
+version: 0.8.0
+inputs:
+  parameters:
+    input: workflow/input.yaml
+  directories:
+    - code
+    - data
+    - workflow
+outputs:
+  files:
+    - results/mass4l_combine_userlvl3.pdf
+workflow:
+  type: snakemake
+  file: workflow/Snakefile
+```
+
+We can now install the REANA command-line client, run the analysis and download the
+resulting plots:
+
+```console
+$ # create new virtual environment
+$ virtualenv ~/.virtualenvs/myreana
+$ source ~/.virtualenvs/myreana/bin/activate
+$ # install REANA client
+$ pip install reana-client
+$ # connect to some REANA cloud instance
+$ export REANA_SERVER_URL=https://reana.cern.ch/
+$ export REANA_ACCESS_TOKEN=XXXXXXX
+$ # create new workflow
+$ reana-client create -n my-analysis
+$ export REANA_WORKON=my-analysis
+$ # upload input code and data to the workspace
+$ reana-client upload
+$ # start computational workflow
+$ reana-client start
+$ # ... should be finished in a couple of minutes
+$ # check its status
+$ reana-client status
+$ # list workspace files
+$ reana-client ls
+$ # download output results
+$ reana-client download
+```
+
+Please see the [REANA-Client](https://reana-client.readthedocs.io/) documentation for
+more detailed explanation of typical `reana-client` usage scenarios.