add a link to the contribution guidelines to make it easier for new people

README

@@ -4,6 +4,7 @@ A personal cloud which runs on your own server.
 http://ownCloud.org
 
 Installation instructions: http://owncloud.org/support
+Contribution Guidelines: http://owncloud.org/dev/contribute/
 
 Source code: https://github.com/owncloud
 Mailing list: https://mail.kde.org/mailman/listinfo/owncloud