Docs review: Allow SmartCard authentication to use SAN extensions

References

Merged MR that introduced documentation requiring review: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/15773 and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/32581/diffs

Related issue(s): https://gitlab.com/gitlab-org/gitlab-ee/issues/8605

Further Details

There was already some review by @eread so maybe it's all good :)