Mention GH Enterprise import support in docs
It's come up twice the past days whether it's possible to import repos from GHE.
The current import docs don't mention this at all https://docs.gitlab.com/ee/workflow/importing/import_projects_from_github.html, whereas it is slightly mentioned in the integration page https://docs.gitlab.com/ee/integration/github.html.
There are two ways to import from GH, via a personal token or when GH auth is enabled. The first option doesn't require any setup in the server's side, whereas the second one does.
We also need to add a note that https://gitlab.com/gitlab-org/gitlab-recipes/tree/master/import/github/enterprise is not officially supported.
@dbalexandre I guess importing from GHE is only possible when GH Auth is enabled, correct?