update to note the app service editor is only in the dedicated plan

Author: gitstua

articles/azure-monitor/app/availability-azure-functions.md

@@ -12,6 +12,7 @@ This article will cover how to create an Azure Function with TrackAvailability()
 
 > [!NOTE]
 > This example is designed solely to show you the mechanics of how the TrackAvailability() API call works within an Azure Function. Not how to write the underlying HTTP Test code/business logic that would be required to turn this into a fully functional availability test. By default if you walk through this example you will be creating a basic availability HTTP GET test.
+> To follow these instructions you must use the [Dedicated Plan](https://docs.microsoft.com/en-us/azure/azure-functions/dedicated-plan) to allow editing code in the App Service Editor
 
 ## Create a timer trigger function