CONTRIBUTING.org: fix typo

Author: nixmaniack

CONTRIBUTING.org

@@ -154,6 +154,10 @@ Contributed configuration layers are stored in the =layers/= folder. The
 =layers/= folder also contains categories prefixed with =+= to put your layers
 in. For example a layer for a language would go in the =layers/+lang/= folder.
 
+Layer with no associated configuration will be rejected. For instance a layer
+with just a package and a hook can be easily replaced by the usage of the
+variable =dotspacemacs-additional-packages=.
+
 *** File header
 The file header for =elisp= files should look like the following template: