(AzureCXP) fixes MicrosoftDocs/azure-docs-pr#487667

Updated line numbers 57-59
From  
No explanation in the article about the difference between using waf_configuration and firewall_policy_id when configuring WAF with Application Gateway in Terraform.  
To  
Added a note clarifying that waf_configuration defines WAF settings inline on the Application Gateway, while firewall_policy_id associates an existing WAF policy resource with the Application Gateway. Only one method should be used in practice.

Author: pradeepmi-MSFT

articles/web-application-firewall/quickstart-web-application-firewall-terraform.md

@@ -54,6 +54,9 @@ The sample code for this article is located in the [Azure Terraform GitHub repo]
 1. Create a file named `main.tf`, and insert the following code:
     :::code language="Terraform" source="~/terraform_samples/quickstart/101-web-application-firewall/main.tf":::
 
+>[!NOTE]  
+> Use `waf_configuration` to define WAF settings directly on the Application Gateway. Use `firewall_policy_id` to associate an existing WAF policy resource with the Application Gateway. Only one method should be used in practice.
+
 1. Create a file named `outputs.tf`, and insert the following code:
     :::code language="Terraform" source="~/terraform_samples/quickstart/101-web-application-firewall/outputs.tf":::