Only schedule frame callback from on_process

draw was called in the pipewire on_process callback, but this is not
safe as libpipewire runs on_process on a separate thread.

Instead, kickstart a frame callback loop if needed and let the
Wayland-side drive drawing on the main thread.

readme: Update discuss section

Move peak_decay to input side

Reflow wl_surface_damage_buffer

Disable werror for now

Move display_dispatch closer to use

Set opaque region

Clean up shm slightly

Switch from EGL to software rendering

Swap ALSA out with PipeWire

Draw on frame callback

layer-shell: Use bottom layer

readme: Elaborate on function

Add README

Initial commit