Can't install LuCI extension (luci-app-mmc-over-gpio)


I was trying to follow to get an SD card mounted in LEDE 17.01.4 but I'm unable to do so via LuCI extension.

I can mount it manually:

block detect > /etc/config/fstab
uci show fstab
uci set fstab.@mount[0].enabled='1'
uci commit
block mount

But I cannot find the corresponding LuCI package "luci-app-mmc-over-gpio"