Add docs/code comments for message-send-flow

app/celery/provider_tasks.py

@@ -91,13 +91,13 @@ def check_sms_delivery_receipt(self, message_id, notification_id, sent_at):
     bind=True, name="deliver_sms", max_retries=48, default_retry_delay=300
 )
 def deliver_sms(self, notification_id):
-    '''
+    """
     This logic will branch off to the final step in delivering
     the notification to sns.
     Logic is in place for delivery receipts.
     Additional logic to help devs output authentication code to
     terminal.
-    '''
+    """
     try:
         current_app.logger.info(
             "Start sending SMS for notification id: {}".format(notification_id)