Update DrawerLayoutAndroid.android.js

Summary:
Currently in the documentation is not clear on how to use the `openDrawer` and `closeDrawer` methods. There is no mention of the requirement to use refs in order to access the Drawer. This should make it clear on how to do the above.
Closes https://github.com/facebook/react-native/pull/13961

Differential Revision: D5479993

Pulled By: hramos

fbshipit-source-id: 4d29f695fbaf097d47f75b345b9998f61156f467

Libraries/Components/DrawerAndroid/DrawerLayoutAndroid.android.js

@@ -270,7 +270,22 @@ var DrawerLayoutAndroid = createReactClass({
       null
     );
   },
-
+  /**
+  * Closing and opening example
+  * Note: To access the drawer you have to give it a ref. Refs do not work on stateless components
+  * render () {
+  *   this.openDrawer = () => {
+  *     this.refs.DRAWER.openDrawer()
+  *   }
+  *   this.closeDrawer = () => {
+  *     this.refs.DRAWER.closeDrawer()
+  *   }
+  *   return (
+  *     <DrawerLayoutAndroid ref={'DRAWER'}>
+  *     </DrawerLayoutAndroid>
+  *   )
+  * }
+  */
   _getDrawerLayoutHandle: function() {
     return ReactNative.findNodeHandle(this.refs[RK_DRAWER_REF]);
   },