feat: fix deprecation warning (#47)

## what
While working in a tf module that uses this module, I got this warning, 

```sh
│ Warning: Deprecated attribute
│ 
│   on .terraform/modules/tailscale_subnet_router/main.tf line 41, in locals:
│   41:   region     = coalesce(var.region, data.aws_region.current.name)
│ 
│ The attribute "name" is deprecated. Refer to the provider documentation for details.
│ 
│ (and 2 more similar warnings elsewhere)
```

Small change to use `id` instead of `name`.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Documentation**
* Added a blank line before the "Requirements" section in the README for
improved readability.

* **Bug Fixes**
* Updated AWS region fallback logic to use the correct identifier,
ensuring accurate region references in configurations.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: westonplatter

README.md

@@ -120,6 +120,7 @@ Use [the awesome `gossm` project](https://github.com/gjbae1212/gossm).
 | [aws_ssm_document.session_logging](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ssm_document) | resource |
 | [null_resource.validate_instance_type](https://registry.terraform.io/providers/hashicorp/null/latest/docs/resources/resource) | resource |
 | [aws_ami.amazon_linux_2023](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/ami) | data source |
+| [aws_ami.instance](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/ami) | data source |
 | [aws_caller_identity.current](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/caller_identity) | data source |
 | [aws_iam_policy_document.default](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/iam_policy_document) | data source |
 | [aws_iam_policy_document.session_logging](https://registry.terraform.io/providers/hashicorp/aws/latest/docs/data-sources/iam_policy_document) | data source |

main.tf

@@ -44,7 +44,7 @@ module "logs_label" {
 }
 
 locals {
-  region     = coalesce(var.region, data.aws_region.current.name)
+  region     = coalesce(var.region, data.aws_region.current.region)
   account_id = data.aws_caller_identity.current.account_id
 
   session_logging_bucket_name = try(coalesce(var.session_logging_bucket_name, module.logs_label.id), "")