Docs & MIDI - no MIDI messages.

Under "Using /dev/umidi* - Testing", an explaination is needed as to what to do to diagnose if no MIDI messages appear on the terminal, despite positive output of `#doas dmesg | tail` and `$ ls /dev/ | grep umidi`.

Likewise, it should be noted that the command "fluidsynth -m oss -a oss SoundFont.sf2" kicks up an error as fluidsynth is not shipped with a soundfont and is looking for one at (which doesn't exist): /usr/local/share/soundfonts/default.sf2
While soundfonts reside in: /usr/local/share/sounds/sf2/ as per:
`# pkg install fluid-soundfont`
An explaination is needed as how to get fluidsynth to look in the correct place...

Start in the “Using /dev/umidi* - Testing” section and reproduce the shown dmesg, device-listing, and fluidsynth commands. Document how to diagnose missing MIDI messages and how the installed soundfont location relates to fluidsynth’s default path; done means both cases have actionable instructions.

Written by the indexing model from the issue text.