Implement Jazzband guidelines for django-waffle

This issue tracks the implementation of the Jazzband guidelines for the project django-waffle

It was initiated by @clintonb who was automatically assigned in addition to the Jazzband roadies.

See the TODO list below for the generally required tasks, but feel free to update it in case the project requires it.

Feel free to ping a Jazzband roadie if you have any question.

TODOs

[x] Fix all links in the docs (and README file etc) from old to new repo
[x] Add the Jazzband badge to the README file
[x] Add the Jazzband contributing guideline to the CONTRIBUTING.md or CONTRIBUTING.rst file
[x] Check if continuous testing works with GitHub Actions
[ ] Check if test coverage is tracked with Codecov
[x] Add jazzband account to PyPI project as maintainer role (e.g. URL: https://pypi.org/manage/project/django-waffle/collaboration/)
[x] Add jazzband-bot as maintainer to the Read the Docs project (e.g. URL: https://readthedocs.org/dashboard/django-waffle/users/)
[ ] Add incoming GitHub webhook integration to Read the Docs project (e.g. URL: https://readthedocs.org/dashboard/django-waffle/integrations/)
[x] Fix project URL in GitHub project description
[x] Review project if other services are used and port them to Jazzband
[x] Decide who is project lead for the project (if at all)
[ ] Set up CI for Jazzband project releases if needed and open ticket if yes