added a few bits regarding casper scripts to docs
added a few bits regarding casper scripts to docs

garris/BackstopJS,klausbayrhammer/BackstopJS,mirzazeyrek/BackstopJS,klausbayrhammer/BackstopJS,garris/BackstopJS,cookchristopher/BackstopJS,cookchristopher/BackstopJS,garris/BackstopJS,mirzazeyrek/BackstopJS