Explicitly import React

Summary:Following this commit:
facebook@a80dd9a
Closes facebook#6910

Differential Revision: D3169295

fb-gh-sync-id: 8a82a7f9dd3b4af2e1cbfdac86842cd450023379
fbshipit-source-id: 8a82a7f9dd3b4af2e1cbfdac86842cd450023379

docs/Tutorial.md

@@ -66,8 +66,10 @@ We're going to render the title, year, and thumbnail for the movie. Since thumbn
 
 ```javascript
 import React, {
-  AppRegistry,
   Component,
+} from 'react';
+import {
+  AppRegistry,
   Image,
   StyleSheet,
   Text,
@@ -304,8 +306,10 @@ First things first: add the `ListView` import to the top of the file.
 
 ```javascript
 import React, {
-  AppRegistry,
   Component,
+} from 'react';
+import {
+  AppRegistry,
   Image,
   ListView,
   StyleSheet,
@@ -391,8 +395,10 @@ There's still some work to be done to make it a fully functional app such as: ad
  */
 
 import React, {
-  AppRegistry,
   Component,
+} from 'react';
+import {
+  AppRegistry,
   Image,
   ListView,
   StyleSheet,