readme update for rails 4.1 [skip ci]
readme update for rails 4.1 [skip ci]

ishumilova/with_advisory_lock,mceachen/with_advisory_lock,BraneLabs/with_advisory_lock,mceachen/with_advisory_lock,ishumilova/with_advisory_lock,ClosureTree/with_advisory_lock,BraneLabs/with_advisory_lock