Added JSX code highlight in Usage section

Author: gebeto

README.md

@@ -53,7 +53,7 @@ npm install react-dat-gui --save
 
 First you'll need a wrapper component which will handle the updates from your dat.GUI, this component should pass the data for the GUI to control as well as an `onUpdate` function to the `DatGui` container component as props. Here's how you might do that:
 
-```
+```jsx
 import '../node_modules/react-dat-gui/build/react-dat-gui.css';
 import React, { Component } from 'react';