message: dist: add a periodic example
diff: -# How to finalize update.
  +# How to finalize updates.
  [updates]
  # String to customize update strategy.
  @@ -10,3 +10,12 @@ strategy = "immediate"
  #strategy = "fleet_lock"
  # Base URL for the FleetLock service.
  #fleet_lock.base_url = "https://fleet-lock.example.com/"
  +
  +# Update strategy which uses a periodic schedule for reboot/maintenance
  +# windows, on a weekly basis.
  +#strategy = "periodic"
  +# Example of reboot windows: weekend days, between 01:00 and 02:00 UTC.
  +#[[updates.periodic.window]]
  +#days = [ "Sat", "Sun" ]
  +#start_time = "01:00"
  +#length_minutes = 60
  