Add example on Components

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

- ActivityIndicator
- TouchableOpacity
- TouchableHighlight

Screenshot on http://localhost:8079/react-native/docs/activityindicator.html
![react-native-activityindicator](https://user-images.githubusercontent.com/13135332/30432801-adca0982-9988-11e7-8e70-94ad9e42ea43.png)

Screenshot on http://localhost:8079/react-native/docs/touchableopacity.html
![react-native-touchableopacity](https://user-images.githubusercontent.com/13135332/30432718-80570554-9988-11e7-9c81-15ab98327fed.png)

Screenshot on http://localhost:8079/react-native/docs/touchablehighlight.html
![react-native-touchablehighlight](https://user-images.githubusercontent.com/13135332/30432733-8290fbb8-9988-11e7-94a1-86c3166e544d.png)
Closes https://github.com/facebook/react-native/pull/15950

Differential Revision: D5881366

Pulled By: hramos

fbshipit-source-id: 2926071723defedf9ed5cb1b1128204256c71dd9

Libraries/Components/ActivityIndicator/ActivityIndicator.js

@@ -36,6 +36,46 @@ type DefaultProps = {
 
 /**
  * Displays a circular loading indicator.
+ *
+ * ### Example
+ *
+ * ```ReactNativeWebPlayer
+ * import React, { Component } from 'react'
+ * import {
+ *   ActivityIndicator,
+ *   AppRegistry,
+ *   StyleSheet,
+ *   Text,
+ *   View,
+ * } from 'react-native'
+ *
+ * class App extends Component {
+ *   render() {
+ *     return (
+ *       <View style={[styles.container, styles.horizontal]}>
+ *         <ActivityIndicator size="large" color="#0000ff" />
+ *         <ActivityIndicator size="small" color="#00ff00" />
+ *         <ActivityIndicator size="large" color="#0000ff" />
+ *         <ActivityIndicator size="small" color="#00ff00" />
+ *       </View>
+ *     )
+ *   }
+ * }
+ *
+ * const styles = StyleSheet.create({
+ *   container: {
+ *     flex: 1,
+ *     justifyContent: 'center'
+ *   },
+ *   horizontal: {
+ *     flexDirection: 'row',
+ *     justifyContent: 'space-around',
+ *     padding: 10
+ *   }
+ * })
+ *
+ * AppRegistry.registerComponent('App', () => App)
+ * ```
  */
 /* $FlowFixMe(>=0.53.0 site=react_native_fb,react_native_oss) This comment
  * suppresses an error when upgrading Flow's support for React. To see the