Add license header to README.

README.md

@@ -1,3 +1,17 @@
+Copyright 2013 Google Inc. All Rights Reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
 # Chrome packaged apps samples
 
 This is the Google Chrome official repository for Chrome packaged apps samples. We have tried to demonstrate most of the [Chrome packaged apps APIs](http://developer.chrome.com/apps/about_apps.html).