added docs for use option

(cherry picked from commit ad5cb0f0d7231ff74d7918faa26091ba710c4709)

lib/ansible/modules/system/service.py

@@ -74,6 +74,12 @@ options:
         description:
         - Additional arguments provided on the command line
         aliases: [ 'args' ]
+    use:
+        description:
+            - The service module actually uses system specific modules, normally through auto detection, this setting can force a specific module.
+            - Normally it uses the value of the 'ansible_service_mgr' fact and falls back to the old 'service' module when none matching is found.
+        default: 'auto'
+        version_added: 2.2
 '''
 
 EXAMPLES = '''