clarify docs for conditional stylesheet use in Rails 3.1+
clarify docs for conditional stylesheet use in Rails 3.1+

nishaya/formtastic,Davidzhu001/formtastic,justinfrench/formtastic,mikz/formtastic,EndingChaung/formtastic,Guestfolio/formtastic,ConferenceCloud/formtastic,ConferenceCloud/formtastic,paulodiovani/formtastic,justinfrench/formtastic,paulodiovani/formtastic,nishaya/formtastic,mikz/formtastic,Baltazore/formtastic,thenthen8515/formtastic,ryanfox1985/formtastic,Guestfolio/formtastic,thenthen8515/formtastic,ryanfox1985/formtastic,sideci-sample/sideci-sample-formtastic,Davidzhu001/formtastic,justinfrench/formtastic,EndingChaung/formtastic,ryanfox1985/formtastic