add some notes on the design

This is just to write down what API should be presented by the
NAS or virutal machine image repository with a list of the
minimum _required_ input and output paramters.
This document does not reflect the current implementation.
commands: placeholder for storageimg command

This is a initial sketch for the command of the storage image
manager
Merge pull request #1 from lclementi/master

Commands for storage manager