Documentation review for the Phabricator Importer

References

Merged MR that introduced documentation requiring review: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27877

Related issue(s): https://gitlab.com/gitlab-org/gitlab-ce/issues/60562

Further Details

The feature is not yet complete, but this is a first blurb so people wanting to contribute know how to enable and see the feature.