doc: update index to match new swh-doc format

related to T1330

docs/index.rst

@@ -15,9 +15,10 @@ information from archive source code artifacts.
    dev-info.rst
 
 
-Indices and tables
-==================
+Reference Documentation
+-----------------------
 
-* :ref:`genindex`
-* :ref:`modindex`
-* :ref:`search`
+.. toctree::
+   :maxdepth: 2
+
+   /apidoc/swh.indexer

[Phabricator Migration user]

Some references in the commit message have been migrated:

• T1330 is now swh-docs#1330