Follow-up from "Fix issue importing members with owner access"

The following discussion from gitlab-ce!28636 should be addressed:

• @jprovaznik started a discussion: (+2 comments)

  Thanks @jameslopez, LGTM 👍. Before merging this one more thought: would it make sense add a note about this behavior into documentation? I see we already have similar type of notes in doc/user/project/settings/import_export.md though not sure what is the best place.

In particular, we may want to have the importer as the owner of the project. See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28636#note_173685093