maintenance.md addition and better suggestions

Created by: LeeNX

Add detail to documentation for satellite creation for omnibus-gitlab users.

Would also be better if the correct suggestion to fix the problem was displayed for omibus-gitlib users, but I don't know where to make them changes, ie

xxxx / reponame ... no
  Try fixing it:
  sudo -u git -H bundle exec rake gitlab:satellites:create RAILS_ENV=production
  If necessary, remove the tmp/repo_satellites directory ...
  ... and rerun the above command
  For more information see:
  doc/raketasks/maintenance.md
  Please fix the error above and rerun the checks.

verse would be better

xxxx / reponame ... no
  Try fixing it:
  sudo gitlab-rake gitlab:satellites:create
  If necessary, remove the tmp/repo_satellites directory ...
  ... and rerun the above command
  For more information see:
  doc/raketasks/maintenance.md
  Please fix the error above and rerun the checks.