docs: Document process for updating Python versions

docs/maintenance.rst

@@ -148,3 +148,16 @@ This section contains useful links for maintainers and collaborators:
 
 - `Future of icalendar, looking for maintainer #360 <https://github.com/collective/icalendar/discussions/360>`__
 - `Comment on the Plone tests running with icalendar <https://github.com/collective/icalendar/pull/447#issuecomment-1277643634>`__
+
+Updating Python Versions
+------------------------
+
+When adding support for a new Python version or removing support for an old one, the following files need to be updated:
+
+1. `.github/workflows/tests.yml`: Add or remove the Python version from the test matrix.
+2. `tox.ini`: Update the `envlist` to include or remove the Python version.
+3. `pyproject.toml`: Update the `requires-python` line and the `classifiers` list.
+4. `README.rst`: Update the compatibility information.
+5. `docs/maintenance.rst`: Update this list if any new files need to be modified.
+
+Remember to test the changes thoroughly and update any documentation that mentions supported Python versions.