Presenting upgrade_levels option

Change-Id: Iaf4d329bc141a5c34ea13f358780318510ce1be1
diff --git a/README.rst b/README.rst
index 213a8b1..239fce5 100644
--- a/README.rst
+++ b/README.rst
@@ -346,6 +346,20 @@
             - aggregate1
             - aggregate2
 
+Upgrade levels
+
+.. code-block:: yaml
+
+    nova:
+      controller:
+        upgrade_levels:
+          compute: juno
+
+    nova:
+      compute:
+        upgrade_levels:
+          compute: juno
+
 SR-IOV
 ------