add instructions on how to use this template

README.md

@@ -6,10 +6,45 @@ The purpose of this repo is to provide a starting point for other software that
 The [Emission Tomography Standardization Initiative (ETSI)](https://etsinitiative.org/)
 is working towards establishing a standard for PET Raw Data, called PETSIRD ("PET ETSI Raw Data").
 
-The specification uses the [yardl](https://aka.ms/yardl) tool to define the model. `yardl` can be used to read the specification (in the `model` directory) and generate an PI for both C++ and API to read/write PETSIRD data.
+The specification uses the [yardl](https://aka.ms/yardl) tool to define the model. `yardl` can be
+used to read the specification (in the `model` directory) and generate an PI for both C++ and API to read/write PETSIRD data.
 
 Currently, a draft model is defined in https://github.com/ETSInitiative/PRDdefinition.
 
-CAVEAT: the draft model generates code in the `prd` namespace. Nevertheless, we have used PETSIRD here
-in most places.
+CAVEAT: the draft model generates code in the `prd` namespace. Nevertheless, we have used the name PETSIRD here
+in most places (except where needed).
+
+## How to use this template?
+
+These instructions will use `YourRepoName` for the name of your new repository. Obviously replace it with something appropriate.
+
+#### Create a new repository based on this template
+
+Easiest is to start from GitHub:
+1. Navigate to the URL of this repo: https://github.com/ETSInitiative/PETSIRDUseCaseTemplate
+2. Click on the `Use this template` button and create your own repo
+3. Pull it to your own local machine and modify
+   1. Search-and-replace all occurences of `PETSIRDUseCaseTemplate` with `YourRepoName`
+   2. Update the README.md to remove references to this template and write something about what your repo is going to do
+   3. Update the `environment.yml`to include what you need. For instance, if you need ROOT, add something like `- root=6.28.0`
+   4. Make some other basic changes and commit
+      ```sh
+      git commit -a -m "Updated template to YourRepoName"
+      git push
+      ```
+
+### Using your repo
+
+1. Open ***your*** repo in [GitHub Codespaces](https://code.visualstudio.com/docs/remote/codespaces) or
+in a [VS Code devcontainer](https://code.visualstudio.com/docs/devcontainers/containers).
+This codespace/container will contain all necessary tools, including `yardl` itself, as well as your repository.
+2. Use `yardl` to generate C++ and Python code for the model:
+  ```sh
+  cd YourRepoName
+  cd PETSIRD/model
+  yardl generate
+  cd ../..
+  ```
+3. Start working in either the [`cpp`](cpp/README.md) and/or [`python`](python/README.md) directories.
+