Add code comment

bakerydemo/base/models.py

@@ -521,6 +521,10 @@ class UserApprovalTaskState(TaskState):
 
 
 class UserApprovalTask(Task):
+    """
+    Based on https://docs.wagtail.org/en/stable/extending/custom_tasks.html.
+    """
+    
     user = models.ForeignKey(
         settings.AUTH_USER_MODEL, on_delete=models.SET_NULL, null=True, blank=False
     )