Merge branch 'develop'

Author: dougalb

docs/source/configuration.rst

@@ -285,7 +285,13 @@ base_os
 """""""
 OS type used in the cluster
 
-Defaults to alinux in the default template. Available options are: alinux, centos6, centos7, ubuntu1404::
+Defaults to alinux in the default template. Available options are: alinux, centos6, centos7, ubuntu1404
+
+Note: The base_os determines the username used to log into the cluster.  
+
+* Centos 6 & 7: ``centos``
+* Ubuntu: ``ubuntu``
+* Amazon Linux: ``ec2-user`` ::
 
     base_os = alinux