update readme

examples/vpc-region-shared-setup/README.md

@@ -39,15 +39,19 @@ Subnets and IDs are not output, so any use of a subnet for selection (say, in an
 the `data aws_subnets` resource with the appropriate filters.
 
 The `variables.vpc.auto.tfvars` needs to be reduced to small number of settings.  It is recommended to follow
-these steps
+these steps to get both files:
 
 ```script
-cp SOURCE/variables.vpc.auto.tfvars variables.vpc.auto.tfvars-from-shared
+mkdir source
+cp SOURCE/variables.{subnets,vpc}.auto.tfvars source/
+
 grep -E "^(shared_vpc_label|vpc_name|vpc_cidr_block|vpc_index|vpc_short_name|vpc_full_name|vpc_environment|vpc_domain_name|vpc_dns_servers|vpc_ntp_servers|tgw_environment) *=" \
-  variables.vpc.auto.tfvars-from-shared > variables.vpc.auto.tfvars
+  source/variables.vpc.auto.tfvars > variables.vpc.auto.tfvars
+
+grep -v ^# source/variables.subnets.auto.tfvars > variables.subnets.auto.tfvars
 ```
 
-This is the set of variable values to be defined (from the shared vpc).
+This is the set of variable values to be defined (from the shared vpc) in `variables.vpc.auto.tfvars`:
 
 ```hcl
 shared_vpc_label = ""
@@ -62,3 +66,12 @@ vpc_dns_servers  = []
 vpc_ntp_servers  = []
 tgw_environment  = ""
 ```
+
+and in `variables.subnets.auto.tfvars`:
+
+```hcl
+public_subnets = []
+private_subnets = [ ]
+```
+
+Fill in the values as approriate from the source of the shared VPC.