DOC: added cookbook.rst to main docs
@wesm @y-p good addition?
 It's a good start, though I suspect the format will ultimately limit this from growing beyond 
a certain point.
Also, you're up against google/stack overflow for discoverability and that's a hard fight.

Possibly a `pandasfu.me` site in the future? a cross between a cheat sheet,
http://repl.it/ and commandlinefu.com.

Suggest putting the word out on the mailing list and opening an eternal issue 
with a "good first PR" tag. **EDIT**: since merging the PR will close this one

Keep knockin'em down, jeff. :thumbsup: 
 ahh....but NOT trying to compete against stackoverflow, in fact lifting links to 'interesting' use cases....
sort of supplemental documentation....
 Oh sure, it's just a question of what people reach for when they hit a problem.
 providing options!
 @y-p what do you think of cookbook? (it just updated)
 Shaping up very nicely.
