Document "machine video" command in the boot(8) man page (offered in 6.2 EFI BOOTX64)

[Tinker]

Hi,

The "OpenBSD/amd64 BOOTX64 3.35" EFI boot console bundled with OpenBSD 6.2 
offers the "video" subcommand to the "machine" command.

Please add it to boot(8).

(The command is not offered by 6.2's MBR boot console.)

Interaction:

     boot> help
     commands: # boot echo env help ls machine reboot set stty time
     machine: diskinfo memory video exit poweroff
     boot> machine video
     Mode 0: 80 x 25
     Mode 1: 80 x 50
     Mode 2: 100 x 31
     Mode 3: 80 x 26
     
     Current mode = 2

And running machine video with an integer argument changes the resolution to 
the respective setting.

Thanks,
Tinker