Added documentation and setup file

I've added a setup file for the MPKminiPlus to use with the program editor for the device, and added some documentation on how to setup/use the controller.

Author: jrb101-musician

docs/devices/akai/mpk.mini.plus.md

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+
+# Akai MPK Mini Plus
+
+## Pre-Setup - Loading the controller configuration file
+
+1. Download the `Akai Professional MPK mini Plus Program Editor` from <https://www.akaipro.com/downloads.html#mpkminiplus>
+
+2. `File -> Open` the `FLStudio2024.mpkminiplus` file in the `Akai Professional MPK mini Plus Program Editor`
+
+3. `File -> Send Program` to `Program 4` which will overwrite the old default for FL Studio with the correct version.
+
+## Setup - Selecting the correct controller program
+
+Continuing from the primary setup instructions.
+
+1. Press the `PROG SELECT` button and use the rotary controller by the OLED screen to select `PGM4: FLStudio2024`.
+
+## Device Details
+
+* In FPC, the banks of drums are mapped as `BANK A` for the bottom 2 rows and `BANK B` for the top row. The pad colours
+  broadly reflect this, but are not currently set dynamically from FPC.
+
+* Currently, there is only a drum pad mode implemented for the pads.
+
+* The 8 rotary encoders are set to endless encode / relative mode and work correctly in plugins supported by the
+  Universal Controller script.
+
+* The transport controls work correctly for `<<`, `>>`, `STOP`, `PLAY` and `REC`. The `SEQ` button is not implemented.
+
+* The Pitch Wheel is mapped to `Channel pitch` in FL Studio and the Mod Wheel is correctly mapped to `MIDI CC 01 - Mod Wheel`
+
+* The joystick can be used to navigate around the mixer channels or the channel rack sequencer buttons. Not sure that
+  is much use but it works.
+
+* This configuration only works on the 1.x series of the Universal Controller script currently. The beta 2.x series breaks
+  the Pitch bend and Mod Wheel linkages when plugins are selected.
+
+## Who to contact
+
+This device is maintained by Jon Baker. [Email](mailto:baker_jon_r@yahoo.co.uk),
+Discord: ***jrb101***.