docs: Add 'local' argument to 'contents'

This means the page title won't be included in the table of contents,
which makes sense. I'm not really sure why this isn't the default, to be
honest.

Signed-off-by: Stephen Finucane <stephen@that.guru>
Signed-off-by: Daniel Axtens <dja@axtens.net>

Author: stephenfin

docs/usage/overview.rst

@@ -4,6 +4,7 @@ Overview
 The key concepts or models of Patchwork are outlined below.
 
 .. contents::
+   :local:
 
 
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