Update release notes

Signed-off-by: Leandro Lucarella <luca-frequenz@llucax.com>

RELEASE_NOTES.md

@@ -10,20 +10,48 @@
 
 ### Cookiecutter template
 
-<!-- Here upgrade steps for cookiecutter specifically -->
+- `mkdocs`
+
+  - The script `docs/mkdocstrings_autoapi.py` was moved to `docs/_scripts/mkdocstrings.py`.
+  - Note that now code annotations will be numbered. This is useful to hint about the order one should read the annotations.
+  - The following files were renamed to keep the documentation directory clean for documentation files:
+
+    - `docs/css` -> `docs/_css`
+    - `docs/overrides` -> `docs/_overrides`
+    - `logo.png` -> `docs/_img/logo.png`
+
+- CI
+
+  - You can now make your branch protection rule only require the "Test with nox" CI job to pass. All the matrix expansions will merge into it, so there is no need to change branch protection rules if matrix elements are added or removed.
 
 ## New Features
 
 <!-- Here goes the main new features and examples or instructions on how to use them -->
 
 ### Cookiecutter template
 
-<!-- Here new features for cookiecutter specifically -->
+- `mkdocs`
+
+  - New markdown extensions: [`def_list` / `task_list`](https://squidfunk.github.io/mkdocs-material/reference/lists/) and [`footnotes`](https://squidfunk.github.io/mkdocs-material/reference/footnotes/).
+  - New [`mkdocs-macros`](https://mkdocs-macros-plugin.readthedocs.io/en/latest/) extension.
+  - Show inherited attributes in the documentation.
+  - Make code annotations numbered. This is useful to hint about the order one should read the annotations.
+  - Updated dependencies.
+
+- CI
+
+  - Add CI job to test package installation on multiple platforms (amd64 and arm64).
+  - Add CI job to run the tests in arm64.
+  - Add a CI job to *join* all `nox` runs, so only one branch protection rule needs to be used.
 
 ## Bug Fixes
 
 <!-- Here goes notable bug fixes that are worth a special mention or explanation -->
 
 ### Cookiecutter template
 
-<!-- Here bug fixes for cookiecutter specifically -->
+- `mkdocs`
+
+  - Fixed mermaid diagrams not rendering in the documentation.
+  - `mypy` ignores for `cookiecutter` have been removed. They should have never be there as generated projects don't use `cookiecutter`.
+  - `mypy` overrides now are applied to API projects too.