added user and password for maas upstream proxy

Change-Id: If48000e957796bf151694f90d37b83c6f8551a51
diff --git a/README.rst b/README.rst
index 178b0c9..6b3548e 100644
--- a/README.rst
+++ b/README.rst
@@ -26,6 +26,8 @@
       upstream_proxy:
         address: 10.0.0.1
         port: 8080
+        user: username      #OPTIONAL
+        password: password  #OPTIONAL
       theme: mirantis
       bind:
         host: 192.168.0.10:5240