Add separate release notes page for v11.0.0

This commit makes a separate page in the generated release note docs
for the v11.0.0 release.

Change-Id: I7dabe26dbe1f08efea2aa99730fde0269b26ce6c
diff --git a/releasenotes/source/index.rst b/releasenotes/source/index.rst
index 5bd9176..b617b22 100644
--- a/releasenotes/source/index.rst
+++ b/releasenotes/source/index.rst
@@ -5,6 +5,7 @@
  .. toctree::
     :maxdepth: 1
 
+    v11.0.0
     v10.0.0
     unreleased