added note to add_hosts about loop bypass

lib/ansible/modules/inventory/add_host.py

@@ -19,6 +19,9 @@ options:
     description:
     - The groups to add the hostname to, comma separated.
     required: false
+notes:
+    - This module bypasses the play host loop and only runs once for all the hosts in the play, if you need it
+    to iterate use a with_ directive.
 author: Seth Vidal
 '''