[VOL-5009] - Create a v2.12 release notes page.

overview/releases.rst
release_notes/index.rst
release_notes/voltha_2.12.rst
-----------------------------
  o Create a skeleton release notes area for v2.12

Change-Id: Ia74075131326e0254af236d9c9edbdf8f46fa430
diff --git a/release_notes/index.rst b/release_notes/index.rst
index 7c3ca31..498fdee 100644
--- a/release_notes/index.rst
+++ b/release_notes/index.rst
@@ -4,6 +4,7 @@
 .. toctree::
    :maxdepth: 1
 
+   voltha_2.12.rst
    voltha_2.11.rst
    voltha_2.10.rst
    voltha_2.9.rst