/**
 * Implements hook_user_role_update().
 */
function {{ machine_name }}_user_role_update($role) {
  // Save extra fields provided by the module to user roles.
  db_merge('my_module_table')
    ->key(array('rid' => $role->rid))
    ->fields(array(
      'role_description' => $role->description
    ))
    ->execute();
}