We set the `HEAD` and eg. `refs/heads/master` refs when updating
repositories, which allows users to easily clone with git.
For now, `HEAD` is chosen based on a unanimity quorum of delegates.
This can be made more sophisticated in the future.
We've also had to ignore some refs during verification, since these
have cropped in for eg. due to the staging copy clone and the
changes included here.
Signed-off-by: Alexis Sellier <alexis@radicle.xyz>