Licensing FAQ: add link to the subscription docs page
Follow up from: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9938#note_149395300
Once https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9938/ has been merged, we should add a link to the licensing FAQ page: https://about.gitlab.com/pricing/licensing-faq/
Edited by Cynthia "Arty" Ng