Add web example (#1717)

Added web example to `Example`

Example/index.js

@@ -3,7 +3,12 @@
  */
 
 import {AppRegistry} from 'react-native';
-import App from './App';
+import App from './src/App';
 import {name as appName} from './app.json';
 
 AppRegistry.registerComponent(appName, () => App);
+
+if (typeof document !== 'undefined') {
+  const rootTag = document.getElementById('root');
+  AppRegistry.runApplication(appName, {rootTag});
+}