Move docs/ to docs/en/

It allows comparison between the directories and helps translations.

docs/en/midi.md

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+# MIDI
+The MIDI module adds keymap entries for sending MIDI data streams. It will require adding the `adafruit_midi` library from the [Adafruit CircuitPython Bundle](https://circuitpython.org/libraries) to your device's folder.  
+Add it to your keyboard's modules list with:
+
+```python
+from kmk.modules.midi import MidiKeys
+keyboard.modules.append(MidiKeys())
+```
+## Keycodes
+
+|Key                            |Description                                               |
+|-------------------------------|----------------------------------------------------------|
+|`KC.MIDI_CC(ctrl, val)`        |Sends a ControlChange message                             |
+|`KC.MIDI_NOTE(note, velo)`     |Sends a Note message                                      |
+|`KC.MIDI_PB(val)`              |Sends a Pitch Wheel message                               |
+|`KC.MIDI_PC(program)`          |Sends a Program Change message                            |
+|`KC.MIDI_START()`              |Sends a Start message                                     |
+|`KC.MIDI_STOP()`               |Sends a Stop message                                      |