Revert moving index.[ios|android].js.

Reverting from 3e2673b -- this broke RN-storybook for `getstorybook` users.

See #1200

examples/ReactNativeVanilla/storybook/stories/index.js

@@ -0,0 +1,25 @@
+import React from 'react';
+import { Text } from 'react-native';
+
+import { storiesOf } from '@storybook/react-native';
+import { action } from '@storybook/addon-actions';
+import { linkTo } from '@storybook/addon-links';
+
+import Button from './Button';
+import CenterView from './CenterView';
+import Welcome from './Welcome';
+
+storiesOf('Welcome', module).add('to Storybook', () => <Welcome showApp={linkTo('Button')} />);
+
+storiesOf('Button', module)
+  .addDecorator(getStory => <CenterView>{getStory()}</CenterView>)
+  .add('with text', () => (
+    <Button onPress={action('clicked-text')}>
+      <Text>Hello Button</Text>
+    </Button>
+  ))
+  .add('with some emoji', () => (
+    <Button onPress={action('clicked-emoji')}>
+      <Text>😀 😎 👍 💯</Text>
+    </Button>
+  ));

lib/cli/generators/REACT_NATIVE/template/storybook/index.ios.js

@@ -0,0 +1,11 @@
+import { AppRegistry } from 'react-native';
+import { getStorybookUI, configure } from '@storybook/react-native';
+
+// import stories
+configure(() => {
+  require('./stories');
+}, module);
+
+const StorybookUI = getStorybookUI({ port: 7007, host: 'localhost' });
+AppRegistry.registerComponent('%APP_NAME%', () => StorybookUI);
+export default StorybookUI;