Update README.md for NPM Install
Update README.md for NPM Install

+ Changes all usage over bower over to npm.
+ Changes references to `./bower_components` to `./node_modules`.

garris/BackstopJS,paleite/BackstopJS,garris/BackstopJS,paleite/BackstopJS,tokimari/BackstopJS,limptwiglet/BackstopJS,thepechinator/BackstopJS,felquis/BackstopJS,pelllich/BackstopJS,limptwiglet/BackstopJS,cookchristopher/BackstopJS,felquis/BackstopJS,klausbayrhammer/BackstopJS,monestereo/BackstopJS,klausbayrhammer/BackstopJS,monestereo/BackstopJS,cookchristopher/BackstopJS,mirzazeyrek/BackstopJS,KMK-ONLINE/BackstopJS,mirzazeyrek/BackstopJS,garris/BackstopJS,KMK-ONLINE/BackstopJS,tokimari/BackstopJS,thepechinator/BackstopJS,pelllich/BackstopJS