Pimoroni Trackball draft module

docs/pimoroni_trackball.md

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+# Pimoroni Trackball
+
+Module handles usage of Trackball Breakout by Pimoroni.
+
+Product page: https://shop.pimoroni.com/products/trackball-breakout
+
+### Usage
+
+Declare I2C bus and add this module in your main class.
+
+```python
+from kmk.modules.pimoroni_trackball import Trackball, TrackballMode
+import bitbangio as io
+
+i2c = io.I2C(scl=board.D3, sda=board.D2)
+trackball = Trackball(i2c, mode=TrackballMode.MOUSE_MODE)
+```
+
+Theoretically, it should work with normal IO library, but I encountered some issues on my RP2040 board.
+
+```python
+import busio as io
+
+i2c = io.I2C(scl=board.D3, sda=board.D2)
+```
+
+Setup backlight color using below commands:
+
+```python
+trackball.set_rgbw(r, g, b, w)
+trackball.set_red(brightness)
+trackball.set_green(brightness)
+trackball.set_blue(brightness)
+trackball.set_white(brightness)
+```
+
+This module exposes one keycode `TB_MODE`, which on hold switches between `MOUSE_MODE` and `SCROLL_MODE`.