Remove unused doc reference

Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

docs/source/index.rst

@@ -5,7 +5,6 @@ Welcome to nexb-skeleton's documentation!
    :maxdepth: 2
    :caption: Contents:
 
-   skeleton-usage
    contribute/contrib_doc
 
 Indices and tables