general questions should be asked on stackoverflow (#1991)

CONTRIBUTING.md

@@ -1,10 +1,15 @@
 ## Contributing
 
 Contributions to the vis.js library are very welcome! We can't do this alone.
+
 You can contribute in different ways: spread the word, report bugs, come up with
 ideas and suggestions, and contribute to the code.
 
-There are a few preferences regarding code contributions:
+If you have any **general question** on how to use the vis.js library in your 
+project please check out 
+[stackoverflow](http://stackoverflow.com/questions/tagged/vis.js) for that.
+
+There are a few preferences regarding **code contributions**:
 
 - vis.js follows the node.js code style as described
   [here](http://nodeguide.com/style.html).