Code:
on !*:JOIN:#chan: {
  if ($read(nicks.txt,w,$+($nick,!*))) return
  write nicks.txt $+($nick,!)
  msg $nick MOTD goes here
}


The ! prefix replaces if ($nick == $me) { halt }

if ($nick isop #channel) { halt } is useless because
noone is ever opped when they join the channel