In README

 - If a session exits too soon, nodm will wait a bit before restarting.  The
   waiting time go as follow:
    - The first time the session exits too soon, restart immediately
    - The second and third time, wait 30 seconds
    - All remaining times, wait 1 minute.
   Once a session lasts long enough, the waiting time goes back to zero.

OK, but do also mention exactly what will be shown on the screen during
those wait periods, how to customize it, and what actions on the
keyboard might have some effects during the wait (e.g., sysrq...?).