Add note in README regarding Array.isArray polyfill for older browsers
Add note in README regarding Array.isArray polyfill for older browsers

kwangkim/classnames,victor-homyakov/classnames,JedWatson/classnames,JedWatson/classnames,ento/classnames,StephenGrider/classnames,longlho/classnames,fattenap/classnames,victor-homyakov/classnames,beni55/classnames,JedWatson/classnames