What you should do is just editing file /etc/wpa_supplicant/wpa_supplicant.conf and add your WIFI information

sudo nano /etc/wpa_supplicant/wpa_supplicant.conf


You should add following text 

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

network={
	ssid="insert_your_hidden_SSID_here"
	scan_ssid=1
	psk="insert_your_wifi_password_here"
	key_mgmt=WPA-PSK
}