Add CONTRIBUTING.md
Add a basic explanation of MVVM to the README
Better diagram images
Fix MS MVVM link
Less douchey intro
Meh, italics
Remove "user input" responsibility of VM

VMs do respond to the user, but not through any direct IBAction or responder chain facility, so it's probably clearer to just leave it out.
Use the word "decoupling" for @joshaber's pleasure
Merge pull request #4 from ReactiveCocoa/brief-explanation

Add a brief MVVM explanation to the README