Add a usage GIF to the README

[srithon]

Currently, there are no visuals in the README and it's just a very long block of text.

[srithon]

I can't seem to figure out how to record my desktop with xrandr adjustments included so this will be backlogged.

[srithon]

We could use a python script to parse the daemon output and graph the brightness over time. Each monitor could have a different color line. This approach would benefit from #42, which would let us control the verbosity of the daemon output.

Another approach would be to have the script run brightness_control --enabled get --brightness in a loop and graph the output over time. This would be significantly easier