Add instructions for contributors

Author: bittner

CONTRIBUTING.rst

@@ -0,0 +1,50 @@
+Contributing
+============
+
+If you want to improve the code base, add a feature or update the
+documentation please open a `pull request`_. Feel free to `open an issue`_
+beforehand to discuss your plans.
+
+.. _pull request: https://github.com/painless-software/python-cli-test-helpers/pulls
+.. _open an issue: https://github.com/painless-software/python-cli-test-helpers/issues
+
+Development
+-----------
+
+This project uses Tox to run its test suite. Install it using Pip like this:
+
+.. code-block:: shell
+
+    python3 -m pip install tox
+
+Alternatively, if you use `uv`_, install Tox as a development tool like this:
+
+.. code-block:: shell
+
+    uv tool install tox --with tox-uv
+
+Usage:
+
+.. code-block:: shell
+
+    tox list             # list available environments
+    tox -e py            # run tests with local default Python
+    tox -e lint,format   # run a few environments
+    tox                  # run entire suite
+
+.. _uv: https://docs.astral.sh/uv/
+
+Documentation
+-------------
+
+Build the documentation locally and view it in your Web browser:
+
+.. code-block:: console
+
+    $ tox -e clean,docs
+    ...
+    $ cd docs/_build/html/
+    $ python -m http.server
+    Serving HTTP on 0.0.0.0 port 8000 (http://0.0.0.0:8000/) ...
+
+Click on the displayed link to inspect the generated documentation.

docs/contributing.rst

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+.. include:: ../CONTRIBUTING.rst

docs/index.rst

@@ -11,6 +11,7 @@ Contents
    tutorial
    other
    techniques
+   contributing
 
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