Fixed comments for running gitlab in a non-root path

• If you don't edit gitlab-shell/config.yml, you wnon't be able to push via SSH (as described here: http://stackoverflow.com/questions/15746336/gitlab-cant-push-code-to-server)
• If you don't re-run sudo -u git -H bundle exec rake assets:precompile RAILS_ENV=production, some icons won't be visible