added comment re: protocol number limitations
added comment re: protocol number limitations

urbit/urbit,urbit/urbit,belisarius222/arvo,jfranklin9000/urbit,jfranklin9000/urbit,ngzax/urbit,belisarius222/arvo,urbit/urbit,jfranklin9000/urbit,jfranklin9000/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,jfranklin9000/urbit,ngzax/urbit,ngzax/urbit,joemfb/arvo,urbit/urbit,joemfb/arvo,urbit/urbit,ngzax/urbit,jfranklin9000/urbit,urbit/urbit,jfranklin9000/urbit,ngzax/urbit