mkdir wifi-firmware
cd wifi-firmware
# Pi 3B
wget https://github.com/RPi-Distro/firmware-nonfree/raw/master/brcm/brcmfmac43430-sdio.bin
wget https://github.com/RPi-Distro/firmware-nonfree/raw/master/brcm/brcmfmac43430-sdio.txt
# Pi 3B+
wget https://github.com/RPi-Distro/firmware-nonfree/raw/master/brcm/brcmfmac43455-sdio.bin
wget https://github.com/RPi-Distro/firmware-nonfree/raw/master/brcm/brcmfmac43455-sdio.clm_blob
wget https://github.com/RPi-Distro/firmware-nonfree/raw/master/brcm/brcmfmac43455-sdio.txt 
sudo cp *sdio* /lib/firmware/brcm/
cd ..