Update CONTRIBUTING.rst

Author: Dario Albanesi

CONTRIBUTING.rst

@@ -5,8 +5,7 @@ Contributing to django CMS
 Like every open-source project, django CMS is always looking for motivated
 individuals to contribute to its source code.
 
-There's more guidance on `how to contribute in our documentation <http://docs.django-cms.org/en/latest/introduction
->`_.
+There's more guidance on `how to contribute in our documentation <http://docs.django-cms.org/en/latest/introduction>`_.
 
 Key points: