update readme with auth options
update readme with auth options

dolph/rack,rackspace/rack,annegentle/rack,DonNateR/rack,dolph/rack,nelsnelson/rack,DonNateR/rack,ryanvz/rack,ryanvz/rack,jarosser06/rack,brint/rack,pratikmallya/rack,jarosser06/rack,jrperritt/rack,annegentle/rack,jrperritt/rack,pratikmallya/rack,brint/rack,rackspace/rack,nelsnelson/rack