Docs faq 348

Resolves: https://github.com/ClusterHQ/flocker/issues/348

Particularly interested in @lukemarsden feedback since he is hearing these questions all the time.
Also, "the glue needing fixing" is somewhat vague (fixing how?). I think the real point is that the core of ZFS is shared with other OSes implementations (Solaris, FreeBSD, etc.) and ZFS on Linux project mostly just works on the glue.