Ability to get image from secured source

PROD-31387

Change-Id: Ic52f473e8f0986a743a911c65d9ac8349e317740
diff --git a/README.rst b/README.rst
index 7bbb04e..ba5e04b 100644
--- a/README.rst
+++ b/README.rst
@@ -620,6 +620,49 @@
    {{- item }}
    %- endfor
 
+Provision VM with secured image source.
+
+.. code-block:: yaml
+
+  salt:
+    control:
+      cluster:
+        mycluster:
+          domain: mydomain.com
+          engine: virt
+          node:
+            ubuntu01:
+              image_source:
+                secured: true
+                protocol: http
+                user: foo
+                password: bar
+                url_prefix: mirror.com
+                url_path: xenial/image.qcow2
+
+Provision several VMs with same secured image source.
+
+  salt:
+    control:
+      common_image_source:
+        protocol: https
+        user: foo
+        password: bar
+        url_prefix: mirror.com
+      cluster:
+        mycluster:
+          domain: mydomain.com
+          engine: virt
+          node:
+            ubuntu01:
+              image_source:
+                secured: true
+                url_path: xenial/ubuntu.qcow2
+            debian01:
+              image_source:
+                secured: true
+                url_path: stretch/debian.qcow2
+
 MCP Cluster health checks
 ~~~~~~~~~~~~~~~~~~~~~~~~~