Raspi WiFi.txt

Edit wpa_supplicant.conf and save it to the root of boot partition.
Replace the country code, ssid, and psk.
Full list of country codes: https://www.thinkpenguin.com/gnu-linux/country-code-list

On first boot, this file will be moved to /etc/wpa_supplicant/wpa_supplicant.conf where it may be edited later.

wpa_supplicant.conf

ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
country=FR

network={
    ssid="<your network name>"
    psk="<your password>"
    key_mgmt=WPA-PSK
}