Document how to upgrade from 6.6.0.pre1.omnibus to 6.6.x.omnibus
We moved two data directories.
# we need to do approximately this
sudo mkdir -p /var/opt/gitlab/git-data
sudo /opt/gitlab/embedded/bin/rsync -av /var/opt/gitlab/{repositories,gitlab-satellites} /var/opt/gitlab/git-data/
sudo /opt/gitlab/embedded/bin/rsync -av /var/opt/gitlab/uploads /var/opt/gitlab/gitlab-rails/