Update readme: Alternative React implementation using refs
Update readme: Alternative React implementation using refs

Alternative React implementation using refs (ES2015 syntax)
As using ReactDOM.findDOMNode is discouraged by facebook
>you can use ReactDOM.findDOMNode as an "escape hatch" but we don't recommend it since it breaks encapsulation
I'm providing an alternative React implementation using ES2015 / TypeScript syntax "using refs", actually it's the preferred (by facebook) "escape hatch" to underlaying DOM nodes: [React: The ref Callback Attribute](https://facebook.github.io/react/docs/more-about-refs.html#the-ref-callback-attribute)
bevacqua/react-dragula,bevacqua/react-dragula