add RW permissions to /dev/gpiochip*

install-gpio-permissions.sh

#!/bin/sh

RULES_TMP_FILE=/tmp/99-gpio-subsystem.rules

# add 'gpio' group
/usr/sbin/addgroup --system gpio

# install udev rules
/usr/bin/echo 'SUBSYSTEM=="gpio", MODE="0660", GROUP="gpio"' > "$RULES_TMP_FILE"
/usr/bin/install --verbose --mode=0644 "$RULES_TMP_FILE" /etc/udev/rules.d/

# apply changes
/usr/bin/udevadm control --reload
/usr/bin/udevadm trigger

# cleanup
/usr/bin/rm -v "$RULES_TMP_FILE"