The old one seems to have stopped working at some point due to all the recent changes to the developer website. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2084>
Document the current code style in HACKING.md, and refer to it in README.md. Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1900>