chore: Add comments to bazzite-steam-runtime so there's no confusion …

…what it's doing or why.

system_files/usr/bin/bazzite-steam-runtime

@@ -1,6 +1,12 @@
 #!/usr/bin/env bash
 
 if [[ "$XDG_SESSION_TYPE" = "wayland" ]] && [[ -e /usr/lib/extest/libextest.so ]]; then
+  # https://github.com/Supreeeme/extest
+  # Extest is a drop in replacement for the X11 XTEST extension.
+  # It creates a virtual device with the uinput kernel module.
+  # It's been primarily developed for allowing the desktop functionality
+  # on the Steam Controller to work while Steam is open on Wayland.
+  # Also supports Steam Input as a whole.
   env LD_PRELOAD=/usr/lib/extest/libextest.so /usr/bin/steam-runtime "$*"
 else
   /usr/bin/steam-runtime "$*"