I've now pushed this to master as
0ea096ae23fa81f05ce97e5e61c15647c0a475ec.

There's still lots to improve, both within the guidance and in addition
to it.

Top on my list is making some requirements about the issues to open when
you want to merge a branch (e.g. specifying the title format so that
qa.guix.gnu.org can detect them).

Thanks,

Chris