First bash at README.

README.md

@@ -1,2 +1,44 @@
-# keybow2040-circuitpython
-CircuitPython library for the Pimoroni Keybow 2040
+# Keybow 2040 CircuitPython
+
+This CircuitPython library is for the RP2040-powered Keybow 2040 from Pimoroni,
+a 16-key mini mechanical keyboard with RGB backlit keys. Find out more about 
+Keybow 2040 at the link below.
+
+[Keybow 2040 at pimoroni.com](https://shop.pimoroni.com/products/keybow-2040).
+
+![Keybow 2040 with backlit keys on marble background](keybow-2040-github-1.jpg)
+
+The library abstracts away most of the complexity of having to check pin states,
+and interact with the IS31FL3731 LED driver library, and exposes classes for
+individual keys and the whole Keybow (a collection of Key instances).
+
+## Getting started quickly!
+
+You'll need to grab the latest version of Adafruit's Keybow 2040-flavoured
+CircuitPython, from the link below.
+
+[Adafruit CircuitPython for Keybow 2040](https://circuitpython.org/board/pimoroni_keybow2040/)
+
+Unplug your Keybow 2040's USB-C cable, press and hold the button on the top edge
+of Keybow 2040 while plugging the USB-C cable back into your computer to mount
+it as a drive (it should show up as `RPI-RP2` or something similar).
+
+Drag and drop the `xxxxxxxx.uf2` file that you downloaded onto the drive and it
+should reboot and load the CircuitPython firmware. The drive should now show up
+as `CIRCUITPY`.
+
+The Adafruit IS31FL3731 LED driver library for CircuitPython is a prequisite for
+this Keybow 2040 library, so you'll need to download it from GitHub at the link
+below, and then drop the `adafruit_is31fl3731` folder into the `lib` folder on
+your `CIRCUITPY` drive.
+
+[Adafruit IS31FL3731 CircuitPython library](https://github.com/adafruit/Adafruit_CircuitPython_IS31FL3731)
+
+Finally, drop the `keybow2040.py` file from this library into the `lib` folder
+on your `CIRCUITPY` drive also, and you're all set!
+
+Pick one of the [examples](examples) (I'd suggest the 
+[reactive.press.py](examples/reactive-press.py) example to begin), copy the 
+code, and save it in the `code.py` file on your `CIRCUITPY` drive using your 
+favourite text editor. As soon as you save the `code.py` file, or make any other
+changes, then it should load up and run the code!

examples/midi-arp.py

@@ -0,0 +1,117 @@
+# SPDX-FileCopyrightText: 2021 Sandy Macdonald
+#
+# SPDX-License-Identifier: MIT
+
+# Demonstrates how to send MIDI notes by attaching handler functions to key
+# presses with decorators.
+
+# You'll need to connect Keybow 2040 to a computer running a DAW like Ableton,
+# or other software synth, or to a hardware synth that accepts USB MIDI.
+
+# NOTE! Requires the adafruit_midi CircuitPython library!
+
+import time
+import board
+import random
+from keybow2040 import Keybow2040
+
+import usb_midi
+import adafruit_midi
+from adafruit_midi.note_off import NoteOff
+from adafruit_midi.note_on import NoteOn
+
+# Set up Keybow
+i2c = board.I2C()
+keybow = Keybow2040(i2c)
+keys = keybow.keys
+
+# Set USB MIDI up on channel 0.
+midi = adafruit_midi.MIDI(midi_out=usb_midi.ports[1], out_channel=5)
+
+# The colour to set the keys when pressed.
+rgb = (255, 50, 0)
+
+# MIDI velocity.
+start_note = 60
+velocity = 127
+
+# Arpeggio style:
+# 0 = up
+# 1 = down
+# 2 = up down
+arp_style = 2
+
+if arp_style == 0 or arp_style == 2:
+    direction = 1
+elif arp_style == 1:
+    direction = -1
+
+last_played = None
+last_pressed = []
+speed = 5
+
+# Loop through keys and attach decorators.
+for key in keys:
+    # If pressed, turn on LED.
+    @keybow.on_press(key)
+    def press_handler(key):
+        key.set_led(*rgb)
+
+    # If released, turn off LED.
+    @keybow.on_release(key)
+    def release_handler(key):
+        key.set_led(0, 0, 0)
+
+while True:
+    # Always remember to call keybow.update()!
+    keybow.update()
+
+    if keybow.any_pressed():
+        pressed = keybow.get_pressed()
+
+        if pressed != last_pressed:
+            notes = [start_note + k for k in pressed]
+            last_pressed = pressed
+
+            if arp_style == 0 or arp_style == 2:
+                this_note = 0
+            elif arp_style == 1:
+                this_note = len(notes) - 1
+
+            midi.send(NoteOn(notes[this_note], velocity))
+            print(notes[this_note])
+
+            last_played = time.monotonic()
+            elapsed = 0
+            last_note = this_note
+            this_note += direction
+
+        else:
+            if notes != []:
+                elapsed = time.monotonic() - last_played
+
+                if elapsed > 1 / speed:
+                    if this_note == len(notes) and direction == 1:
+                        this_note = 0
+                    elif this_note < 0:
+                        this_note = len(notes) - 1
+
+                    midi.send(NoteOff(notes[last_note], 0))
+                    midi.send(NoteOn(notes[this_note], velocity))
+                    print(notes[this_note])
+
+                    last_played = time.monotonic()
+                    last_note = this_note
+
+                    if arp_style == 2 and this_note == len(notes) -1:
+                        direction = -1
+                    elif arp_style == 2 and this_note == 0:
+                        direction = 1
+
+                    this_note += direction
+
+    elif len(last_pressed) and keybow.none_pressed():
+        for note in range(128):
+            midi.send(NoteOff(note, 0))
+
+        last_pressed = []