Document to discuss the nobrainer API This has come up in a few issues that we need to start producing a high level API interface for nobrainer, in addition to the lower level interfaces. Primary audience: users of nobrainer models - think scripters more than developers. Other users will have command line interfaces (via nobrainer zoo) that they can use in shell. Those interfaces should also mimic as much of this API as possible. Proposal: Principles Keep API surface as close to scikit-learn and nilearn as possible to maximize community reuse