[docs] Add react-dnd

Follow mui#3103. This topic has quite some activity.
I think it's great to lead the community in this direction.

Author: oliviertassinari

docs/src/app/components/pages/discover-more/related-projects.md

@@ -17,3 +17,4 @@ Addon for storybook.
 A React component for swipeable views. Plays well with the `Tabs` component.
 - [UniversalRelayBoilerplate](https://github.com/codefoundries/UniversalRelayBoilerplate)
 Boilerplate + examples for React Native (iOS, Android), React (isomorphic, Material-UI), Relay, GraphQL, JWT, Node.js, Apache Cassandra.
+- [react-dnd](http://gaearon.github.io/react-dnd/examples-sortable-simple.html) Drag and Drop for React.