add README

README.md

@@ -3,10 +3,54 @@
 The first 4K intro for the Raspberry Pi Pico.  
 Wild compo entry released at Function 2022.
 
-## Building
+## Platform
 
-TODO
+Raspberry Pi Pico - 264 KB RAM, 2 MB flash, 125+ MHz CPU (easily overclockable
+to 250 MHz and more)
 
-## Running
+The [Pico Demo Base](https://shop.pimoroni.com/products/pimoroni-pico-vga-demo-base)
+seems to be the standard way to do demo stuff on the Pico, it conveniently has
+everything you need (VGA, PWM Audio, a few buttons). KiCad schematics are
+[available](https://datasheets.raspberrypi.org/rp2040/VGA-KiCAD.zip) to build
+your own since ordering it is expensive.
 
-TODO
+This demo only uses the passive parts of the Pico Demo Base, everything else is unused:
+- the VGA "DAC" resistor ladder
+- the PWM Audio resistor-capacitor signal path
+
+## Building and Flashing
+
+Dependencies:
+
+- CMake
+- arm-none-eabi-gcc
+- [pico-sdk](https://github.com/raspberrypi/pico-sdk) (run `git submodule update --init`)
+- [exomizer](https://bitbucket.org/magli143/exomizer) (expected to be in PATH when compiling)
+
+Compile with:
+
+```
+cmake -B build -DCMAKE_BUILD_TYPE=MinSizeRel .
+cd build && make
+```
+
+Flash via any of these methods:
+
+- `picotool load build/proj/pico4k.bin -t bin`
+- `picotool load build/proj/pico4k.uf2`
+- drag `pico4k.uf2` onto the Pico's virtual flash drive in bootloader mode
+
+## Pinout for manual Setup
+
+If you don't have a Pico Demo Board or just want to feel the joy of having a
+mess of wires on a breadboard that works, here are the detailed pinouts:
+
+- VGA Red: GPIO 0-4 (0 is LSB)
+- not connected: GPIO 5
+- VGA Green: GPIO 6-10 (6 is LSB)
+- VGA Blue: GPIO 11-15 (11 is LSB)
+- VGA HSync: GPIO 16
+- VGA VSync: GPIO 17
+- not connected: GPIO 18-26
+- Audio Right: GPIO 27
+- Audio Left: GPIO 28