Audio docs point to non-existant file for midi information

[jetpacktuxedo]

https://docs.qmk.fm/#/feature_audio?id=midi-functionality points to quantum/keymap_midi.c which is not a thing that exists.

[noroadsleft]

quantum/keymap_midi.c was removed in 65faab3. It seems to have been refactored into quantum/process_keycode/process_midi.c and quantum/process_keycode/process_midi.h, but I'm not nearly skilled enough in C to know if that's actually the case.

[drashna]

Yup, it was refactored.

Now.... do I add full documentation, or just update the line.

[jetpacktuxedo]

I mean, if you're up to writing full docs then I'd definitely suggest doing that, but imo updating the line would close this issue while actually documenting the midi stuff would be a separate one.