SGB sound page contains some mistakes

according to some research i have done, with some help from @leinacc, there is no "jump packet", instead it seems to just be a termination code. to actually jump somewhere you need to do one of:
- inject a `jmp` at either `$0635` or `$0e74`, then write `$00` to all 4 ports (otherwise the SNES locks up)
- `jump` to SNES code that communicates with the SPC
- mis-use `sound`, which was **not** tested and *probably* wont actually work

the page also calls the N-SPC driver "the SNES MIDI engine", which is misleading, despite the format being somewhat similar to MIDI (or so i heard)

lastly, if the first "packet"s length is 0, its instead treated as a length of 65536, which almost certainly will lock up the SPC (guess how i found out)