Creamos el fichero:

rootfs/etc/NetworkManager/system-connections/<MiId>.nmconnection

[connection]
id=<MiId>
type=wifi
interface-name=wlan0

[wifi]
mode=infrastructure
ssid=<MiRed>

[wifi-security]
key-mgmt=wpa-psk
psk=<TuContraseñaWiFi>

[ipv4]
method=auto

[ipv6]
method=ignore