Hi Stef,
my latest image has all you need onboard.
rm /srv/http/command/rune_shutdown
ln -s /srv/http/command/rune_shutdown.audiophonics /srv/http/command/rune_shutdown
systemctl enable sds
It uses the following GPIOs:
"ShutDown : GPIO17=in, Low"
"BootOK : GPIO22=out, High"
Frank