chore(travis): add badge to readme (#166)

README.md

 # Angular 2 QuickStart Source
+[![Build Status][travis-badge]][travis-badge-url]
 
 This repository holds the TypeScript source code of the [angular.io quickstart](https://angular.io/docs/ts/latest/quickstart.html),
 the foundation for most of the documentation samples and potentially a good starting point for your application.
@@ -148,3 +149,6 @@ A custom reporter (see `protractor.config.js`) generates a  `./_test-output/prot
 which is easier to read; this file is excluded from source control.
 
 Shut it down manually with Ctrl-C.
+
+[travis-badge]: https://travis-ci.org/angular/quickstart.svg?branch=master
+[travis-badge-url]: https://travis-ci.org/angular/quickstart