Add initial resources.md for discussion

The first draft of a Kubernetes resource model.
The context in which a request is made or a usage is recorded can be arbitrarily complex (e.g. "request for pod XYZ" or "daily average usage of all pods with labels matching this selector, on June 27th, with EWMA with weight 27.1, clipped to the range [0,32]". )  That makes me think that the first representation is better.