MAN: Document that client_idle_timeout can't be shorter than 10 seconds
    
    To ensure the client timeout is not too low and clients do not reconnect
    too often, the client_idle_timeout is forced to be 10 seconds minimum.
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>