service: document CreateService.

service.go

@@ -104,7 +104,8 @@ type Config struct {
 	//  * OS X
 	//    - KeepAlive     bool (true)
 	//    - RunAtLoad     bool (false)
-	//    - UserService bool (false) // Install as a current user service.
+	//    - UserService   bool (false) - Install as a current user service.
+	//    - SessionCreate bool (false) - Create a full user session.
 	Option KeyValue
 }