Add initial resources.md for discussion

The first draft of a Kubernetes resource model.
re: not relying on borrowed resources  ... correct behavior

Agree, I would not argue "nobody should be specifying limits".  In fact I argue the opposite - that limit should be implied to == request by default, rather than (as specced) unlimited.  I think DTRT means don't encourage the users to hurt themselves, and that means not making it easy to accidentally rely on borrowed resources.

Or at least (I'm going to hate this) that decision should be made per-resources.  We know from internal experience that allowing people to use "spare" CPU cycles is good for utilization and performance overall, but bad for capacity planning, benchmarking, and consistent behavior.  I could see making that the default for CPU.  We also know that allowing people to use "spare" memory is eventually disastrous for almost everyone.  we should not make that a default.

Maybe the default for limit is dependent on whether the resource is compressible?