updating README with gem/plugin installation instructions
updating README with gem/plugin installation instructions

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