[4.0] 40112d5 reference to wiki page

[Nils Goroll]

commit 40112d580e27501df3e297ff2f5cd586a02b4a2c
Author: Nils Goroll <nils.goroll at uplex.de>
Date:   Tue Mar 18 16:51:44 2014 +0100

    reference to wiki page

diff --git a/CONTRIBUTING b/CONTRIBUTING
index cfccc09..2c2db8c 100644
--- a/CONTRIBUTING
+++ b/CONTRIBUTING
@@ -1,6 +1,9 @@
 Contributing to Varnish Cache
 =============================
 
+To contribute to Varnish, read https://www.varnish-cache.org/trac/wiki/Contributing
+as a staring point and follow relevant parts linked there.
+
 Varnish Cache is developed with Git hosted on our own infrastructure.
 
 Official development tree is here: