update webhook documentation

clarify inability to use security certificates with webhook.

Author: jacegummersall

articles/azure-monitor/alerts/action-groups.md

@@ -632,7 +632,7 @@ For information about pricing for supported countries/regions, see [Azure Monito
 
 > [!NOTE]
 >
-> If you use the webhook action, your target webhook endpoint needs to be able to process the various JSON payloads that different alert sources emit. If the webhook endpoint expects a specific schema, for example, the Microsoft Teams schema, use the Logic Apps action to transform the alert schema to meet the target webhook's expectations.
+> If you use the webhook action, your target webhook endpoint needs to be able to process the various JSON payloads that different alert sources emit. You can not pass security ceritifcate through a webhook action. If the webhook endpoint expects a specific schema, for example, the Microsoft Teams schema, use the Logic Apps action to transform the alert schema to meet the target webhook's expectations.
 
 Webhook action groups use the following rules: