Add release instructions

Author: seddonym

CONTRIBUTING.rst

@@ -147,4 +147,21 @@ Run cargo flamegraph on the relevant test. E.g. to profile ``rust/tests/large.rs
 
 ``sudo cargo flamegraph --root --test large``
 
-This will create a file called ``flamegraph.svg``, which you can open to view the flamegraph.
+This will create a file called ``flamegraph.svg``, which you can open to view the flamegraph.
+
+Releasing to Pypi
+=================
+
+1. Choose a new version number (based on `semver <https://semver.org/>`_).
+2. ``git pull origin master``
+3. Update ``CHANGELOG.rst`` with the new version number.
+4. Update the ``release`` variable in ``docs/conf.py`` with the new version number.
+5. Update the ``__version__`` variable in ``src/grimp/__init__.py` with the new version number.
+6. Update ``project.version`` in ``pyproject.toml`` with the new version number.
+7. ``git commit -am "Release v{new version number"``
+8. ``git push``
+9. Wait for tests to pass on CI.
+10. ``git tag v{new version number}``
+11. ``git push --tags``
+12. This should kick start the Github ``release`` workflow, which builds wheels and releases the
+    project to PyPI.