doc: document [HHMM] option

Author: ensc

README.org

@@ -17,9 +17,11 @@ reconnect.
 * Usage
 
 #+BEGIN_SRC sh
-/usr/sbin/dhcpd-pd ppp0 /etc/dhcpd-pd/run
+/usr/sbin/dhcpd-pd ppp0 /etc/dhcpd-pd/run [HHMM]
 #+END_SRC
 
+- =HHMM= is optional and specifies the time of the daily reconnect
+
 * Scripts
 
 see [[https://gitlab.com/ensc-groups/bpi-router/tools/setup/-/blob/master/files/dhcpd-pd/run][run]] for a sample script.