Added reference to the line "ENV['RAILS_RELATIVE_URL_ROOT'] = "/gitlab"" , as it talked about in the gitlab.yml.example
Updated at the request of @f0k
Changed wording in application.rb and gitlab.yml.example to match unicorn.rb. This is for when using a non-root path
Merge pull request #4902 from misilot/missing-config-unicorn.rb

Add hints for relative URL installation