Add initial resources.md for discussion

The first draft of a Kubernetes resource model.
+1. While I appreciate the insight, I agree that this document should focus more on the expression of resource requests, limits, and capacity. Resource usage monitoring could be spec'ed out separately.
If, on the other hand, you are proposing that a Kubernetes client would specify its pod's predicted resource usage based on previous traces or expert systems, and that a scheduler/isolator would use more than the min/max to estimate pod fit feasibility, optimal pod co-locations, and/or optimal balancing of excess resources between multiple co-located pods growing beyond their requested resources, then I am prepared to have my mind blown with the advanced resource tweaking going on inside Google. (Even still, it may belong in a resource shapes v2 doc.)
Perhaps we're just unclear on how/when you expect these histograms to be used. Enlighten us, please.