Fixed forgottent reference to old mailing lists.

src/site/markdown/contributing.md

@@ -19,7 +19,7 @@ without charges, in your applications, and that you can improve it and have
 your improvements included in the next mainstream release.
 
 If you are interested in participating in the development effort,
-subscribe to the mailing lists and step up to discuss it. The
-larger the community is, the better Orekit will be. The main
-rule is that everything intended to be included in Orekit core must
-be distributed under the Apache License Version 2.0.
+subscribe to the forums (as described in the [Contact page](./contact.html)) 
+and step up to discuss it. The larger the community is, the better Orekit
+will be. The main rule is that everything intended to be included in Orekit
+core must be distributed under the Apache License Version 2.0.