Add initial resources.md for discussion

The first draft of a Kubernetes resource model.
Why do we want to allow the user to set limit and not request?  I think the spec gets simpler if we just say that fields are cumulative in their effect.

absent request, absent limit => choose sane defaults for me
present request, absent limit => limit = request
absent request, present limit = error

It's not a huge deal, I just don't see why we should go out of the way to handle obviously invalid input.