More descriptive name for one of the new optional variables

AWS/Terraform/terraform.tfvars.example

@@ -6,5 +6,5 @@ public_key_path = "/home/user/.ssh/id_logger.pub"
 private_key_path = "/home/user/.ssh/id_logger"
 ip_whitelist = ["1.2.3.4/32"]
 availability_zone = "us-west-1b"
-// tag_prefix = "some_prefix_"
+// instance_name_prefix = "some_prefix_"
 // custom-tags = {"tag_name": "tag_value"}