Add section numbering to some of the larger subdocuments.
diff --git a/Doc/library/index.rst b/Doc/library/index.rst
index 717bfb8..f25724c 100644
--- a/Doc/library/index.rst
+++ b/Doc/library/index.rst
@@ -38,6 +38,7 @@
 
 .. toctree::
    :maxdepth: 2
+   :numbered:
 
    intro.rst
    functions.rst