Inky Frame: Document buttons & LEDs.

Expand upon memoryview caveat with Inky 7.3.

micropython/modules_py/inky_frame.md

@@ -5,6 +5,8 @@ Most of your interaction with Inky Frame will be via the PicoGraphics library, b
 - [Pico Graphics](#pico-graphics)
   - [Colour \& Dithering](#colour--dithering)
   - [Images \& JPEGs](#images--jpegs)
+- [Buttons \& LEDs](#buttons--leds)
+  - [Status LEDs](#status-leds)
 - [Battery Power \& RTC](#battery-power--rtc)
   - [Function Reference](#function-reference)
     - [Wakeup States](#wakeup-states)
@@ -60,6 +62,38 @@ You can use the `jpegdec` (JPEG decoding) module to display JPEG files on Inky,
 2. JPEGs are, by default, dithered to the 7 (or 8 on 4.0 and 5.7) available colours. This uses "ordered dither," which is fast, but not very pretty.
 3. You can turn off dithering with `jpeg.decode(dither=False)` for a posterised effect.
 
+## Buttons & LEDs
+
+Inky Frame has five user buttons labelled A to E, with LEDs. The buttons are connected via a shift-register and available in the `inky_frame` module as `button_a`, `button_b`, `button_c`, `button_d` and `button_e`.
+
+Each button has some convenient methods for checking if it's pressed:
+
+* `raw()` - get the current state of the button with no debounce (returns `True` the first time it's called if the corresponding button)
+* `read()` - read the current button state, observing debounce (50ms)
+
+Additionally each button has some methods for controlling its associated LED:
+
+* `led_on()` - turn the LED on
+* `led_off()` - turn the LED off
+* `led_toggle()` - toggle the LED
+* `led_brightness(0.5)` - set the LED brightness (from 0.0 to 1.0)
+
+### Status LEDs
+
+In addition to the button LEDs there are two status LEDs, `busy` and `wifi`, which are available as:
+
+* `led_busy` - connected to pin `LED_BUSY`
+* `led_wifi` - connected to pin `LED_WIFI`
+
+These are instances of the `pimoroni.PWMLED` class, and have the following methods:
+
+* `on()` - turn the LED on
+* `off()` - turn the LED off
+* `toggle()` - toggle the LED
+* `brightness(0.5)` - set the LED brightness (from 0.0 to 1.0)
+
+:info: `toggle()` is provided for compatibility with the `Pin()` class. It's a little odd, since it changes the LED brightness to `1.0 - current_brightness`.
+
 ## Battery Power & RTC
 
 When running on battery power, Inky Frame's buttons cause it to wake from a power-off state and start running your code. Additionally an onboard PCF85063A real-time clock runs continuously from battery and can wake up your Frame automatically.
@@ -127,4 +161,4 @@ PicoGraphics has undocumented support for accessing its raw framebuffer using `m
 
 This is useful for copying raw binary images (effectively valid Inky frame buffers saved to a file) avoiding JPEG compression and so forth. For some dicussion about why and how you might do this, see: https://github.com/pimoroni/pimoroni-pico/issues/681
 
-This *does not work* for Inky 7.3, since there is no framebuffer in memory.
+:warning: This *does not work* for Inky 7.3, since there is no framebuffer in memory. PicoGraphics will raise a `ValueError: No local framebuffer.` if you try. We aim to fix this with some hardfault handling sorcery.