add checklist

vpc-transit-gateway-association/README.md

@@ -18,6 +18,16 @@ section TGW setup, consisting of data (required), self, and peer (remote(s)).  T
 Use of this set of modules and configuration requires Terraform 1.x and the Terraform Provider v4.x.  If you have the AWS provider pinned with a `version = "~> 3.66"` statement
 you'll ned to change that to `version = ">= 4.0"`.
 
+# Setup Checklist
+
+-[ ] convert VPC to tf 1.x
+-[ ] change provider pinning in `versions.tf`
+-[ ] have access to network account via standard profile
+-[ ] ensure `tgw_environment` is defined on `module.vpc`
+-[ ] ensure an `attachmnet` subnet (/28 pe AZ) is defined and labelled
+-[ ] use output from `module.subnets` or construct the proper input list of objects
+-[ ] call data, use output as input to self, then peer (self required first)
+
 # Setup
 
 Due to the nature of some of the data resources and `for_each` not being able to be determined properly, this is split into three