Documented availability of 'auth' tag

Change-Id: I06ffd3a9237df881986967376d81d11e9c9f4f98
diff --git a/README.rst b/README.rst
index c027b1a..f00ce6c 100644
--- a/README.rst
+++ b/README.rst
@@ -16,6 +16,7 @@
   run_tests.sh --nova
   run_tests.sh --glance
   run_tests.sh --swift
+  run_tests.sh --auth
 
 
 Additional Info