add Book example

Add example from @CamDavidsonPilon to front page. 
cf deployed on my fork here : http://gistpynb.herokuapp.com/

Btw, this book has been linked on [Pycoders Weekly](http://us4.campaign-archive2.com/?u=9735795484d2e4c204da82a29&id=c812fb6f4d&e=db2b52b812).