Add timer usage for es6

Author: sunnylqm

docs/Timers.md

@@ -73,4 +73,25 @@ var Component = React.createClass({
 });
 ```
 
-We strongly discourage using the global `setTimeout(...)` and recommend instead that you use `this.setTimeout(...)` provided by react-timer-mixin. This will eliminate a lot of hard work tracking down bugs, such as crashes caused by timeouts firing after a component has been unmounted.
+This will eliminate a lot of hard work tracking down bugs, such as crashes caused by timeouts firing after a component has been unmounted.
+
+However, `TimerMixin` and any other mixins *can not be used in ES6*. But don't worry, what TimerMixin does is really simple - clearing every timer used when current component is going to unmount. So you can manually do this like the following example: 
+
+```javascript
+import React,{
+  Component
+} from 'react-native';
+
+export default class Hello extends Component {
+  componentDidMount() {
+    this.timer = setTimeout(
+      () => { console.log('save the timer ref to this, which can be cleared later'); },
+      500
+    );
+  }
+  componentWillUnmount() {
+    // if this.timer exits, then use clearTimeout to clear it.
+    this.timer && clearTimeout(this.timer);
+  }
+};
+```