Make it more obvious to use the Gitea backend for Forgejo/Codeberg

[mavit]

I tried to follow the instructions at https://anitya.readthedocs.io/en/latest/contributing.html#docker-podman but couldn't get it working, so these changes are untested.

[softwarefactory-project-zuul[bot]]

Build failed. More information on how to proceed and troubleshoot errors available at https://fedoraproject.org/wiki/Zuul-based-ci https://fedora.softwarefactory-project.io/zuul/buildset/1332e985b45a46bcb267b0907e38cd22

:heavy_check_mark: fi-tox-mypy SUCCESS in 5m 10s :heavy_check_mark: fi-tox-lint SUCCESS in 5m 15s :heavy_check_mark: fi-tox-format SUCCESS in 5m 14s :x: fi-tox-python310 FAILURE in 8m 06s :x: fi-tox-python311 FAILURE in 8m 35s :x: fi-tox-python312 FAILURE in 8m 45s :heavy_check_mark: fi-tox-docs SUCCESS in 5m 20s :heavy_check_mark: fi-tox-bandit SUCCESS in 5m 16s :x: fi-tox-diff-cover FAILURE in 9m 24s

[Zlopez]

I tried to follow the instructions at https://anitya.readthedocs.io/en/latest/contributing.html#docker-podman but couldn't get it working, so these changes are untested.

What issue did you hit? Also you should be able to just run tox tests without the need to run the docker environment.