adjust error message

main.tf

@@ -638,7 +638,7 @@ resource "azurerm_kubernetes_cluster" "main" {
     }
     precondition {
       condition     = var.private_dns_zone_id == null ? true : (anytrue([for r in local.valid_private_dns_zone_regexs : try(regex(r, reverse(split("/", var.private_dns_zone_id))[0]) == reverse(split("/", var.private_dns_zone_id))[0], false)]))
-      error_message = "Private DNS zone must be in one of the following format: `privatelink.<region>.azmk8s.io`, `<subzone>.privatelink.<region>.azmk8s.io`, `private.<region>.azmk8s.io`, `<subzone>.private.<region>.azmk8s.io`"
+      error_message = "According to the [document](https://learn.microsoft.com/en-us/azure/aks/private-clusters?tabs=azure-portal#configure-a-private-dns-zone), the private DNS zone must be in one of the following format: `privatelink.<region>.azmk8s.io`, `<subzone>.privatelink.<region>.azmk8s.io`, `private.<region>.azmk8s.io`, `<subzone>.private.<region>.azmk8s.io`"
     }
   }
 }