op-build v1.21.1 release notes

Signed-off-by: Stewart Smith <stewart@linux.vnet.ibm.com>
diff --git a/doc/release-notes/index.rst b/doc/release-notes/index.rst
index c1ba934..1912751 100644
--- a/doc/release-notes/index.rst
+++ b/doc/release-notes/index.rst
@@ -9,3 +9,4 @@
    v1.21-rc1
    v1.21-rc2
    v1.21
+   v1.21.1