Add Travis badge

Author: kevinsawicki

README.md

@@ -1,5 +1,7 @@
 # <img src="https://cloud.githubusercontent.com/assets/378023/15172388/b2b81950-1790-11e6-9a7c-ccc39912bb3a.png" width="60px" align="center" alt="Electron API Demos icon"> Electron API Demos
 
+[![Build Status](https://travis-ci.org/electron/electron-api-demos.svg?branch=master)](https://travis-ci.org/electron/electron-api-demos)
+
 This is a desktop app that interactively and with sample code demonstrates core features of the [Electron](http://electron.atom.io) API. It's built with Electron, too, of course. This app works on Windows, OS X and Linux operating systems.
 
 Use this app to see what you can do with Electron and use the source code to learn how to create a basic Electron app.