Updated readme.

Author: Martin Brecht-Precht

README.md

@@ -62,6 +62,11 @@ $renderer->render($qrCodeData, 'path/to/qr-code.eps');
 
 ---
 
+## Contribution
+
+Contributing to our projects is always very appreciated.  
+**But: please follow the contribution guidelines written down in the `CONTRIBUTING.md` document.**
+
 ## TODOs
 
 - Decorate the code base with some unit tests.