Add README with first example

modules/net-ncc/README.md

@@ -0,0 +1,65 @@
+# Network Connectivity Center Module
+
+This module allows the creation and management of an NCC-based hub-and-spoke architecture. It focuses in site-to-cloud connectivity with network virtual appliances (NVAs) as the _backing resource_ for spokes. This allows to connect an external network to Google Cloud by using a SD-WAN router or another appliance with BGP capabilities. It does not handle site-to-site data transfer which is not available in all regions, in particular in EMEA.
+
+The module can manage a hub, multiple spokes, and corresponding Cloud Routers and BGP sessions to network virtual appliances. The NVAs themselves, VPCs, and other Google Cloud resources should be handled externally.
+
+## Examples
+
+### Connect a site to a VPC network
+
+In this example a router appliance connects with a peer router in an on-premises network, and also peers with a Cloud Router.
+
+```hcl
+module "vpc" {
+  source     = "./fabric/modules/net-vpc"
+  project_id = "my-project"
+  name       = "network-a"
+  subnets = [
+    {
+      name          = "subnet-a"
+      ip_cidr_range = "10.1.3.0/24"
+      region        = "us-central1"
+    }
+  ]
+}
+
+module "nva1" {
+  source     = "./fabric/modules/compute-vm"
+  project_id = "my-project"
+  zone       = "us-central1-a"
+  name       = "router-app-a"
+  network_interfaces = [{
+    network    = module.vpc.self_link
+    subnetwork = module.vpc.subnet_self_links["us-central1/subnet-a"]
+    addresses  = {external = null, internal = "10.1.3.8"}
+  }]
+  can_ip_forward = true
+}
+
+module "ncc" {
+  source     = "./fabric/modules/net-ncc"
+  asn        = 65000
+  name       = "ncc-hub"
+  project_id = "my-project"
+  spokes = {
+    spoke_A = {
+      vpc        = module.vpc.name
+      region     = "us-central1"
+      subnetwork = module.vpc.subnet_self_links["us-central1/subnet-a"]
+      nvas = [
+        {
+          vm = module.nva1.self_link
+          ip = module.nva1.internal_ip
+        }
+      ]
+      router = {
+        ip1       = "10.1.3.14"
+        ip2       = "10.1.3.15"
+        peer_asn  = 65001
+      }
+    }
+  }
+}
+# tftest
+```