Clarify spec vs status, and what we plan to do with usage.

The title here is "status", but the contents is "usage".  Let's move this "usage" description to the appendix, where it's more naturally a TBD.

Do we have a plan to have a resourceStatusSpec, which would describe what has actually been allocated?  If so, that belongs here.  If not, then we don't need to talk about status - the implication being that status==request.