Add doc to setup a valid api key

Workaround for api limit

Author: Elie CHARRA

README.md

@@ -10,7 +10,7 @@ It's built with Electron, Node.js, Angular.js, and uses the Soundcloud API.
 
 Follow us on twitter for updates [@Soundnodeapp](https://www.twitter.com/soundnodeapp).
 
-Featured on [Producthunt](https://www.producthunt.com/tech/soundnode-2), [TNW](http://thenextweb.com/apps/2016/01/25/soundnode-is-the-soundcloud-desktop-app-youve-been-waiting-for/#gref) 
+Featured on [Producthunt](https://www.producthunt.com/tech/soundnode-2), [TNW](http://thenextweb.com/apps/2016/01/25/soundnode-is-the-soundcloud-desktop-app-youve-been-waiting-for/#gref)
 and [Gizmodo](http://gizmodo.com/soundnode-turns-soundcloud-into-a-spotify-like-desktop-1754953529)
 
 ![alt tag](https://raw.githubusercontent.com/Soundnode/soundnode-app/master/Soundnode-app.png)
@@ -28,6 +28,17 @@ and [Gizmodo](http://gizmodo.com/soundnode-turns-soundcloud-into-a-spotify-like-
 
 And much more!
 
+## Configuration
+
+Since soundcloud apply rate limit to third party app you need to configure your own API key to make soundnode work.
+
+Unfortunatly soundcloud suspended new application creation, so to retrieve your api key, you have to dig into soundcloud website.
+
+* Login to soundcloud.com on favorite browser
+* Look for and api call and write down the client_id parameter
+![dev tools](doc/img/dev_tools.png)
+* Edit your userConfig.json file (see here for location : https://github.com/eliecharra/soundnode-app/blob/master/app/public/js/common/configLocation.js#L34) and update clientId parameter with the previously retrieved one.
+
 ## How to contribute
 
 First, building, testing, and reporting bugs is highly appreciated. Please include console's output and steps to reproduce the problem in your bug report if possible.