Docs improvement

Summary:
In the `Additional Scenes` section, the `TouchableHighlight` component is used, but is not present in the import statement.

This is confusing and results in a `Can't find variable: TouchableHighlight` error.

This PR attempts to correct this confusion.
Closes https://github.com/facebook/react-native/pull/10276

Differential Revision: D3997058

Pulled By: hramos

fbshipit-source-id: 22ebf39cd39d8a76427c89cecc774ff9aef2c3c8

Libraries/CustomComponents/Navigator/Navigator.js

@@ -141,7 +141,7 @@ var GESTURE_ACTIONS = [
  *
  * ```
  * import React, { Component } from 'react';
- * import { Text, Navigator } from 'react-native';
+ * import { Text, Navigator, TouchableHighlight } from 'react-native';
  *
  * export default class NavAllDay extends Component {
  *   render() {