Adding the contributing.md from archivista

CONTRIBUTING.md

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+# Contributing to Witness
+
+We welcome contributions from the community and first want to thank you for
+taking the time to contribute!
+
+Before starting, please take some time to familiarize yourself with the [Code of Conduct](CODE_OF_CONDUCT.md).
+
+
+## Getting Started
+
+We welcome many different types of contributions and not all of them need a
+Pull Request. Contributions may include:
+
+* New features and proposals
+* Documentation
+* Bug fixes
+* Issue Triage
+* Answering questions and giving feedback
+* Helping to onboard new contributors
+* Other related activities
+
+### Setting up your environment
+
+### Required Tooling
+Some tools are required on your system in order to help you with
+the development process:
+
+* Git: Witness is hosted on GitHub, so you will need to have Git installed. For
+ more information, please follow [this guide](https://github.com/git-guides/install-git).
+
+* GNU Make: The root of the directory contains a `Makefile` for automating development
+ processes. The `make` CLI tool is usually installed by default on most systems
+ (excluding Windows), but you can check if it is installed by running `make --version`
+ on your terminal. If this command is unsuccessful, you will need to find the standard
+ method for installing it for your system. For installing `make` on Windows, please see
+ [here](https://gnuwin32.sourceforge.net/packages/make.html).
+
+* Go v1.19: Witness is written in [Go](https://golang.org/), so you 
+ will need this installed in order to compile and run the source code.
+
+#### Getting the Witness source code
+
+[Fork](https://docs.github.com/en/get-started/quickstart/fork-a-repo>) the repository on GitHub and
+[clone](https://docs.github.com/en/repositories/creating-and-managing-repositories/cloning-a-repository) it to
+your local machine: 
+```console
+    git clone [email protected]:YOUR-USERNAME/witness.git
+```
+*The command above uses SSH to clone the repository, which we recommend. You can find out more
+about how to set SSH up with Github [here](https://docs.github.com/en/authentication/connecting-to-github-with-ssh).*
+
+
+Add a [remote](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/configuring-a-remote-for-a-fork) and
+regularly [sync](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork) to make sure
+you stay up-to-date with our repository:
+
+```console
+    git remote add upstream https://github.com/in-toto/witness.git
+    git checkout main
+    git fetch upstream
+    git merge upstream/main
+```
+
+### Running Tests
+
+You can run all the tests by executing the command:
+
+```console
+    make test
+```