Add guide to taint certificate

Author: ringanta

README.md

@@ -45,6 +45,15 @@ module "acm" {
 - [Basic usage example](./examples/basic/)
 - [Use existing domain validations records](./examples/without-domain-validation)
 
+## Recreating ACM Certificate
+
+Due to the [https://github.com/terraform-providers/terraform-provider-aws/issues/8531](https://github.com/terraform-providers/terraform-provider-aws/issues/8531) issue, this module implement a workaround that makes existing ACM certificate won't be recreated when we change the subject alternatives name. So make sure to taint the certificate using `terraform taint` command before adjusting the subject alternatives name. Here is the steps:
+
+1. Taint exisiting certificate using `terraform taint module.acm.aws_acm_certificate.self` command.
+1. Adjust value of the `subject_alternatives_name` variable.
+1. Run `terraform plan -out=tfplan.out` and review the execution plan.
+1. Apply the change using `terraform apply tfplan.out`.
+
 ## Inputs
 
 | Name | Description | Type | Default | Required |