add documentation for MIDI setup

[nnirror]

Some folks might need to set up MIDI drivers on their machine before they can pipe Facet into a DAW. I should add steps to the documentation :)

[nnirror]

I'm pretty sure the issue here is the default assigning of a MIDI output. When there are none available on a machine, the MIDI output is set to undefined. I think I'll need to rework this line: https://github.com/mjcella/facet/blob/main/js/facet_server.js#L24

[nnirror]

This commit should fix the fatal error: 92b537e

[nnirror]

This commit documents MIDI troubleshooting: e8d0da9

And with that, closing it out 👍