Modify S6329: Make GCP sample safer (#2529)

rules/S6329/terraform/rule.adoc

@@ -105,11 +105,17 @@ For GCP:
 ----
 resource "google_compute_instance" "example" {
   network_interface {
-    network = "default"
+    network = google_compute_network.vpc_network_example.name
   }
 }
 ----
 
+Note that setting `network="default"` in the network interface block leads to
+other security problems such as removal of logging, Cloud VPN/VPC network
+peering, and the addition of insecure firewall rules. +
+A safer alternative includes creating a specific VPC or subnetwork and enforce
+security measures.
+
 include::../see.adoc[]
 
 ifdef::env-github,rspecator-view[]