Update README to document attribute for packages to remove
Update README to document attribute for packages to remove

Document the attribute controlling the list of packages to remove,
including the default value (which preserves the existing behaviour).

hardening-io/chef-os-hardening,rollbrettler/chef-os-hardening,rollbrettler/chef-os-hardening,mikemoate/chef-os-hardening,8x8Cloud/chef-os-hardening,hardening-io/chef-os-hardening,8x8Cloud/chef-os-hardening,mikemoate/chef-os-hardening