added required missing field for common yaml fmt

lib/ansible/plugins/inventory/generator.py

@@ -15,6 +15,10 @@ DOCUMENTATION = '''
         - Every element of every layer is combined to create a host for every layer combination
         - Parent groups can be defined with reference to hosts and other groups using the same template variables
     options:
+      plugin:
+         description: token that ensures this is a source file for the 'generator' plugin.
+         required: True
+         choices: ['generator']
       hosts:
         description:
           - The C(name) key is a template used to generate