docs: update header.md of the root module

Author: Rahul-4480

.header.md

@@ -12,7 +12,6 @@ This Terraform module automates the deployment of the Atlantis server on an ECS
 
 ## Prerequisites
 
-- Domain with ACM certificate attached
 - Application secrets stored in AWS SSM Parameter Store with the following names and descriptions:
   - `/atlantis/ATLANTIS_GH_TOKEN`: A GitHub personal access token with repo and admin:repo_hook permissions. Generate this from GitHub Developer settings.
   - `/atlantis/ATLANTIS_GH_WEBHOOK_SECRET`: The secret used to validate GitHub webhooks. Create a random secret string for this.