Update 'Auth indicators' doc string
    
    The doc string located in the 'Authentication
    indicators' ('Services' settings page) was
    missing the usage explanation for the 'ipd'
    checkbox option.
    
    Fixes: https://pagure.io/freeipa/issue/9338
    Signed-off-by: Carla Martinez <carlmart@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>