Include instructions for node

Author: JMPerez

README.md

@@ -53,6 +53,18 @@ The wrapper includes helper functions to do the following:
 Install via bower (browser):
 
     $ bower install spotify-web-api-js
+    
+Install via node (since the requests are made using XMLHttpRequest, you will need a tool like Browserify to run this on a browser):
+
+    $ npm install spotify-web-api-js
+
+Then, in your javascript file
+
+```javascript
+var Spotify = require('spotify-web-api-js');
+var s = new Spotify();
+//s.searchTracks()...
+```
 
 or by making a copy of the `src/spotify-web-api.js` file