README.md: Add note about OpenWrt fork
README.md: Add note about OpenWrt fork

Note that we're a fork.

Signed-off-by: Daniel Dickinson <360a5f079379974c7f45f9f4c8b6bbd2e549553c@cshore.thecshore.com>

cshore/luci,cshore/luci,cshore-firmware/openwrt-luci,cshore-firmware/openwrt-luci,cshore/luci,cshore/luci,cshore/luci,cshore-firmware/openwrt-luci,cshore-firmware/openwrt-luci,cshore-firmware/openwrt-luci,cshore/luci,cshore-firmware/openwrt-luci,cshore/luci,cshore/luci,cshore-firmware/openwrt-luci,cshore-firmware/openwrt-luci