Fix README typo in firewall module (#960)

* fixing readme in firewall module

* fix typo

Co-authored-by: Valerio Ponza <vponza@google.com>
Co-authored-by: Ludovico Magnocavallo <ludo@qix.it>

modules/net-vpc-firewall/README.md

@@ -138,10 +138,10 @@ module "firewall" {
   project_id       = "my-project"
   network          = "my-network"
   factories_config = {
-
+    rules_folder  = "config/firewall"
+    cidr_tpl_file = "config/cidr_template.yaml"
   }
-  data_folder        = "config/firewall"
-  cidr_template_file = "config/cidr_template.yaml"
+
 }
 # tftest skip
 ```