Add initial resources.md for discussion

The first draft of a Kubernetes resource model.
There's at least two places where defaults can apply.  There's the API into the apiserver and the API into the kubelet.  Do we expect the same defaults at both edges, or can, for example, the kubelet be more restrictive?  This is how we specced internally - the master can decide the defaulting behavior and the 'let expected an absolute answer.

E.g. if the master said "default is unbounded" it would pass 2^64 to the 'let.