docs(examples/spi-st7789-rpi-zero-w): update readme

mipidsi/examples/spi-st7789-rpi-zero-w/README.md

@@ -1,12 +1,32 @@
 # SPI ST7789 on a Raspberry Pi Zero W Example
 
-Tested with [Display HAT Mini by Pomoroni](https://shop.pimoroni.com/products/display-hat-mini?variant=39496084717651).
+This example demonstrates how to use the [Display HAT Mini by Pomoroni](https://shop.pimoroni.com/products/display-hat-mini?variant=39496084717651) on a Raspberry Pi Zero W.
+
+The example shows a scrolling text and a pulsing RGB LED.
+
+Buttons:
+
+- A: change LED color
+- B: exit
+- X: move text up
+- Y: move text down
+
+## Pre-requisite
+
+**Enable SPI** by any of this options:
+
+- `sudo raspi-config`
+- `sudo raspi-config nonint do_spi 0`
+- manually adding `dtparam=spi=on` to /boot/config.txt
+- the graphical Raspberry Pi Configuration UI
+
+[More info about SPI](https://docs.golemparts.com/rppal/0.14.1/rppal/spi/index.html#spi0)
 
 ## Build, strip, copy, and run
 
 ### Mac OS
 
-Prerequisite: musl-cross (Homebrew users: `brew install filosottile/musl-cross/musl-cross`)
+Pre-requisite: musl-cross (Homebrew users: `brew install FiloSottile/musl-cross/musl-cross --without-x86_64 --with-arm-hf`)
 
 ```bash
 # build for rpi zero w