Adding Pump API stuff to the docs index.

This commit sponsored by Joel Luellwitz.  Thanks!

docs/source/index.rst

@@ -96,6 +96,26 @@ This chapter contains various information for developers.
    devel/migrations
 
 
+Part 5: Pump API
+================
+
+This chapter covers MediaGoblin's `Pump API
+<https://github.com/e14n/pump.io/blob/master/API.md>`_ support.  (A
+work in progress; full federation is not supported at the moment, but
+media uploading works!  You can use something like
+`PyPump <http://pypump.org>`_
+to write MediaGoblin uploadable applications.)
+
+.. toctree::
+   :maxdepth: 1
+
+   api/client_register
+   api/oauth
+   api/media
+   api/media_interaction
+
+
+
 Indices and tables
 ==================