[Doc] Terraform disables auto mount of ServiceAccount token

User brought up an issue where the operator did not start because the service account token was missing:

https://forums.couchbase.com/t/couchbase-operator-1-2-upgrade/21325/6

And it turns out that in terraform "AutomountServiceAccountToken is hardcoded to false"

https://github.com/terraform-providers/terraform-provider-kubernetes/issues/38

Not exactly sure where to document this, could be in the known issues or note on the operator install steps.