Default branch for storing the publiccode.yml file

[libremente]

Discussion

Since there are no indications whether the default branch where to store the publiccode.yml file has to be master, maybe the standard should provide more details.
This may be a problem when a repository does not have a branch named master.

[sebbalex]

This needs to be addressed as soon as we can. Many projects are turning to a different default branch naming convention.
cc @libremente @bfabio @alranel

[bfabio]

Many projects are turning to a different default branch naming convention.

Also GitHub is planning on having main as the default branch soon

[bfabio]

The obvious and backward compatible thing to do would be adding an optional branch key, but the standard is (purposely?) vague on which VCS are supported, but explicitly references Subversion.

Now, Subversion can address branches in its URLs and I think this is true for Bazaar and Mercurial as well, unlike git.

Do we want to define the supported VCSs in url so we can make better informed decisions with branch key or do we want to be generic and future proof?

If we pick the former we can name the new key gitBranch and have validations in place for invalid cases like using SVN with or without a branch in the URL and a non-empty gitBranch.

If we pick the latter, branch would be "branch for all the VCS that don't allow addressing branches in their URL, ie git 90% of the times".