docs: Add release instructions for maintainers (#61)

* Detail how to use bump2version to make a new release tag and then check the test release on TestPyPI before releasing through GitHub releases.

docs/maintainer-notes.md

@@ -0,0 +1,46 @@
+# Notes for maintainers
+
+## Making a new release
+
+To make a new release of `recast-atlas` a maintainer should execute the following workflow:
+
+1. Verify that you're on the project default branch and are synced with GitHub
+
+```console
+$ git checkout master && git pull
+```
+
+2. Use `bump2version` to bump the version and create a commit and tag
+
+```console
+$ bump2version <part>
+```
+
+3. Push the commit and the tag to GitHub, triggering a distribution to be built and published to [TestPyPI](https://test.pypi.org/project/recast-atlas/).
+
+```console
+$ git push --tags
+```
+
+4. Got to [TestPyPI](https://test.pypi.org/project/recast-atlas/) to check that the release page looks okay. If you want to verify that the sdist and wheel are valid you can either download them manually or with
+
+```console
+$ python -m pip download --extra-index-url https://test.pypi.org/simple/ --pre recast-atlas
+```
+
+or you can install them with
+
+```console
+$ python -m pip install --upgrade --extra-index-url https://test.pypi.org/simple/ --pre recast-atlas
+```
+
+to perform local tests.
+
+5. Once satisfied with the TestPyPI version, a release can be made through GitHub. Go to the project releases page: https://github.com/recast-hep/recast-atlas/releases
+
+6. Click "Draft a new release".
+
+7. On the new page enter the tag you just pushed (e.g. `v0.1.0`) in the "Tag version" box and the "Release title" box (to make it easy unless you really want to get descriptive).
+
+8. Enter any release notes and click "Publish release".
+   * This then kicks of the publication CD workflow that will use the PyPI API key to publish.