Docs: add note that TF S3 config bucket needs name changed

Suggest adding something similar to this:

   - Review [terragrunt.hcl](./terragrunt.hcl). Make the `remote_state.config.bucket` name globally unique to satisfy this requirement of S3 buckets. If this step is skipped, the `terragrunt` commands below will fail to locate, create, or access the configuration S3 bucket.

In the terraform Quickstart section with the other Review the configuration steps.

I tried deploying the terraform module without doing this and encountered the errors referenced above. I'd suggest this via an MR but do not have that level of access.