Add documentation in README and some metadata

Cargo.toml

@@ -3,6 +3,10 @@ name = "pixelfoo-viewer"
 version = "0.1.0"
 authors = ["Juergen Stuber <juergen@jstuber.net>"]
 description = "Viewer for pixelfoo frame streams."
+homepage = "https://codeberg.org/poc/pixelfoo-viewer.git"
+repository = "https://codeberg.org/poc/pixelfoo-viewer.git"
+keywords = ["led", "led-matrix", "neopixel", "smart-leds", "cli", "graphics", "2d"]
+categories = ["graphics"]
 license = "MIT OR Apache-2.0"
 edition = "2021"
 

README.md

@@ -2,6 +2,40 @@
 
 > A viewer for pixelfoo frame streams.
 
+## Background
+
+At Chaospott in Essen we have a large 80x40 array of Neopixel LEDs
+in the ceiling our main room.
+A server can run various apps to generate animations on the LED array.
+
+## Apps
+
+Apps can be written in any programming language,
+they are started as child processes.
+They get the width and height as the first and second command line parameter,
+plus currently one additional free-to-use third parameter.
+
+Apps generate a stream of fixed format pixel data as their standard output.
+A pixel is either three bytes for red, green and blue (RGB),
+or four bytes with additionally white (RGBW).
+The number of pixels specified by the width make up a row,
+and the number of rows specified by the height make up a frame.
+Frames are sent consecutively, without any additional delimiters.
+
+The app controls the speed by the timing of the frame data it sends.
+
+## Viewer
+
+The viewer runs such apps locally and displays the animation in a window.
+This helps with app development.
+
+For example,
+```
+pixelfoo-viewer -w apps/backlight.py 80 40
+```
+runs the `backlight.py` app (assuming it exists) in RGBW mode
+with an 80x40 matrix.
+
 ## License
 
 Licensed under either of