docs: simplify conf.py and fix compatibility with upcoming Sphinx 6.0

Change-Id: I970c5691cb4b1879854023a3747c2bf63189c128
diff --git a/docs/index.rst b/docs/index.rst
index bdd22a2..a7f9d90 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -1,13 +1,13 @@
-ChronoSync - A synchronization Protocol in NDN
-==============================================
+ChronoSync - A Synchronization Protocol for NDN
+===============================================
 
 .. toctree::
    :hidden:
    :maxdepth: 3
 
-   DesignDoc
+   design
 
-* :doc:`DesignDoc`
+* :doc:`design`
 * `API documentation (doxygen) <doxygen/annotated.html>`_
 
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