added docs for referenceUrl
added docs for referenceUrl

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