Add Example for TouchableOpacity.js

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Adding example with [react-native-web-player](https://github.com/dabbott/react-native-web-player)

Screenshot on http://localhost:8079/react-native/docs/touchableopacity.html
![react-native-touchableopacity](https://user-images.githubusercontent.com/13135332/30335218-bd32fb0e-9807-11e7-976d-5235402fdba8.png)
Closes https://github.com/facebook/react-native/pull/15911

Differential Revision: D5817180

Pulled By: TheSavior

fbshipit-source-id: 6399a53dabf8e3f0cf680aeb41d8afbaa2ce11e8

Libraries/Components/Touchable/TouchableOpacity.js

@@ -51,6 +51,72 @@ var PRESS_RETENTION_OFFSET = {top: 20, left: 20, right: 20, bottom: 30};
  *   );
  * },
  * ```
+ * ### Example
+ *
+ * ```ReactNativeWebPlayer
+ * import React, { Component } from 'react'
+ * import {
+ *   AppRegistry,
+ *   StyleSheet,
+ *   TouchableOpacity,
+ *   Text,
+ *   View,
+ * } from 'react-native'
+ *
+ * class App extends Component {
+ * constructor(props) {
+ *  super(props)
+ *  this.state = { count: 0 }
+ * }
+ *
+ * onPress = () => {
+ *   this.setState({
+ *     count: this.state.count+1
+ *   })
+ * }
+ *
+ *  render() {
+ *     return (
+ *       <View style={styles.container}>
+ *         <TouchableOpacity
+ *          style={styles.button}
+ *          onPress={this.onPress}
+ *        >
+ *          <Text> Touch Here </Text>
+ *        </TouchableOpacity>
+ *        <View style={[styles.countContainer]}>
+ *          <Text style={[styles.countText]}>
+ *             { this.state.count !== 0 ? this.state.count: null}
+ *           </Text>
+ *         </View>
+ *       </View>
+ *     )
+ *   }
+ * }
+ *
+ * const styles = StyleSheet.create({
+ *   container: {
+ *     flex: 1,
+ *     justifyContent: 'center',
+ *     paddingHorizontal: 10
+ *   },
+ *   button: {
+ *     alignItems: 'center',
+ *     backgroundColor: '#DDDDDD',
+ *     padding: 10
+ *   },
+ *   countContainer: {
+ *     alignItems: 'center',
+ *     padding: 10
+ *   },
+ *   countText: {
+ *     color: '#FF00FF'
+ *   }
+ * })
+ *
+ * AppRegistry.registerComponent('App', () => App)
+ * ```
+ *
  */
 var TouchableOpacity = createReactClass({
   displayName: 'TouchableOpacity',