Add separate release notes page for 12.0.0

This commit splits out a release notes page for the 12.0.0 release
that was recently pushed just as we have done with every other major
version.

Change-Id: I06f9d027199203acb2b855190a7555fca3ff68c8
diff --git a/releasenotes/source/index.rst b/releasenotes/source/index.rst
index b617b22..2c22408 100644
--- a/releasenotes/source/index.rst
+++ b/releasenotes/source/index.rst
@@ -5,6 +5,7 @@
  .. toctree::
     :maxdepth: 1
 
+    v12.0.0
     v11.0.0
     v10.0.0
     unreleased
diff --git a/releasenotes/source/v12.0.0.rst b/releasenotes/source/v12.0.0.rst
new file mode 100644
index 0000000..0bc8343
--- /dev/null
+++ b/releasenotes/source/v12.0.0.rst
@@ -0,0 +1,6 @@
+=====================
+v12.0.0 Release Notes
+=====================
+
+.. release-notes:: 12.0.0 Release Notes
+   :version: 12.0.0