clarify bcrypt cost doc
clarify bcrypt cost doc

lukeasrodgers/authlogic,sideci-sample/sideci-sample-authlogic,nulogy/authlogic,janusnic/authlogic,antonifs/authlogic,tiegz/authlogic,boone/authlogic,bioritmo/authlogic,nebulab/authlogic,manvil/authlogic,expertiza/authlogic,theiren46/authlogic,binarylogic/authlogic,jaredbeck/authlogic,Photovisi/authlogic,rchekaluk/authlogic