The image does not include drivers for the on-board wifi as they are proprietary. You will need a USB wifi adapter such as those from ThinkPenguin.com. An Atheros AR9271 based adapter was used in this example (USB ID 0cf3:9271)
# ip a
# wpa_passphrase MYSSID passphrase > /etc/wpa_supplicant/wpa_supplicant.conf- there will be no prompt to type, just type your wifi password and press Enter.
# cat /etc/wpa_supplicant.confto check the newly generated config file
# wpa_supplicant -B -i wlan0 -c /etc/wpa_supplicant/wpa_supplicant.conf
The connection should now be up, check with
ip a or
ping yahoo.com for example.