docs+build: Prepare release of version 0.4.0

Change-Id: Ie5dfb3a1c7674cd426b89721c91ad59327517764
Refs: #3178
diff --git a/docs/index.rst b/docs/index.rst
index eaa0cb7..fcfc521 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -19,7 +19,14 @@
    examples
    tutorials
    manpages
+
+.. toctree::
+   :hidden:
+   :maxdepth: 1
+
    code-style
+   RELEASE_NOTES
+   releases
 
 - :doc:`README`
 
@@ -37,14 +44,15 @@
 
 - :doc:`manpages`
 
-Documentation for ndn-cxx developers and contributors
-+++++++++++++++++++++++++++++++++++++++++++++++++++++
+**Additional documentation**
 
 - `API documentation (doxygen) <doxygen/annotated.html>`_
 
 - :doc:`code-style`
 
-- :doc:`Release Notes <RELEASE_NOTES>`
+- :doc:`RELEASE_NOTES`
+
+- :doc:`releases`
 
 License
 -------