pkg/js: add link to example

pkg/js/README.md

 Methods and annotations to specify interoperability with JavaScript APIs.
 
 *Note: This package is beta software.*
 
 *Note: This packages requires Dart SDK `>=1.13.0-dev.7`.*
 
 ### Adding the dependency
 
 Add the following to your `pubspec.yaml`:
 
 ```yaml
 dependencies:
   js: ^0.6.0-beta
 ```
 
 #### Passing functions to JavaScript.
 
 If you are passing a Dart function to a JavaScript API, you must wrap it using
 `allowInterop` or `allowInteropCaptureThis`.
 
 ### Examples
 
+There is a [full example](https://github.com/dart-lang/sdk/tree/master/pkg/js/example) hosted with the `package:js` source code.
+
 #### Calling methods
 
 ```dart
 // Calls invoke JavaScript `JSON.stringify(obj)`.
 @Js("JSON.stringify")
 external String stringify(obj);
 ```
 
 #### Classes and Namespaces
 
@@ skipping 52 matching lines @@
 ## Contributing and Filing Bugs
 
 Please file bugs and features requests on the [Github issue tracker](https://github.com/dart-lang/js-interop/issues).
 
 We also love and accept community contributions, from API suggestions to pull requests.
 Please file an issue before beginning work so we can discuss the design and implementation.
 We are trying to create issues for all current and future work, so if something there intrigues you (or you need it!) join in on the discussion.
 
 Code contributors must sign the
 [Google Individual Contributor License Agreement](https://developers.google.com/open-source/cla/individual?csw=1).