The separation between the `develop` and `main` branches was inherited
from Tusky and isn't helpful, complicating the release process and
causing CI to repeatedly run the same actions on the same code.
Deprecate the `develop` branch by removing references to it in the
documentation and updating the CI configuration as necessary.
Separately, the GitHub settings will be changed to set `main` as the
default branch, and the `develop` branch will be deleted.
e0e4235354