Adds steps for running GitLab Pages on a separate server
What does this MR do?
Our GitLab Pages documentation briefly mentions that it is possible to run Pages daemon on a standalone server, but there are no exact instructions how to configure it.
This MR adds the section about configuring GitLab Pages on a separate server.
Related to https://gitlab.com/gitlab-org/gitlab-ce/issues/33096#note_31468939 and gitlab-pages#144 (closed).