fix getting started with terraform doc (#1224)

website/content/en/preview/getting-started-with-terraform/_index.md

@@ -86,6 +86,7 @@ module "vpc" {
 
   private_subnet_tags = {
     "kubernetes.io/cluster/${var.cluster_name}" = "owned"
+    "karpenter.sh/discovery" = var.cluster_name
   }
 }
 
@@ -134,6 +135,14 @@ terraform apply -var cluster_name=$CLUSTER_NAME
 
 Everything should apply successfully now!
 
+### Create the EC2 Spot Service Linked Role
+
+This step is only necessary if this is the first time you're using EC2 Spot in this account. More details are available [here](https://docs.aws.amazon.com/batch/latest/userguide/spot_fleet_IAM_role.html).
+```bash
+aws iam create-service-linked-role --aws-service-name spot.amazonaws.com
+# If the role has already been successfully created, you will see:
+# An error occurred (InvalidInput) when calling the CreateServiceLinkedRole operation: Service role name AWSServiceRoleForEC2Spot has been taken in this account, please try a different suffix.
+```
 
 ### Configure the KarpenterNode IAM Role