Fix unexpanded numref

We need to number subsection all the way to the lowest level to prevent
our :numref:s from not having a number to refere to.

index.rst

@@ -2,7 +2,7 @@ SANE Standard
 =============
 
 .. toctree::
-   :numbered: 3
+   :numbered: 4
    :maxdepth: 3
    :caption: Contents: