Add some explanation

[chrisspruck]

Hey Ed - I had to look up "Cognitive Behavior Therapy tool". I don't think I'm qualified to do a PR for this, but perhaps in the README, you could add a brief paragraph on what one is for, what yours does, etc. I saw some articles and tools, but I wouldn't know enough to recognize a good resource, other than maybe the Wikipedia definition (http://en.wikipedia.org/wiki/Cognitive_behavioral_therapy).