Add ability to set reauthentication_auth_method option

To allow heat to reauthenticate using trusts for long running tasks
this option is needed to be set to 'trusts'.

Change-Id: I48c36487aee5cde5fd3cf139766038fecd7e3f28
Related-Prod: https://mirantis.jira.com/browse/PROD-27017
diff --git a/README.rst b/README.rst
index f443584..32fa6eb 100644
--- a/README.rst
+++ b/README.rst
@@ -23,6 +23,7 @@
         enabled: true
         version: icehouse
         region: RegionOne
+        reauthentication_auth_method: trusts
         bind:
           metadata:
             address: 10.0.106.10