Explain how to contribute to the project
The Contributing page is unreachable and outdated. https://cubicweb.readthedocs.io/en/stable/#how-to-contribute could be converted into its own page. The branching and versioning solution described in https://hedgedoc.logilab.fr/reQOETFWRGSDV9G3TiELRA# should be added to the contributing page.
Add a CONTRIBUTING.rst/md to the cubicweb repository.