To add network info you need to create a second text file called wpa_supplicant.conf and place that in the root of the boot SD too.

Run Notepad
Paste in the contents below (adjusting for the name of your country code, network name and network password):

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

network={
   ssid="NETWORK-NAME"
   psk="NETWORK-PASSWORD"
}
Click File / Save As ...

Be sure to set Save as type to All Files (so the file is NOT saved with a .txt extension)
Call the file wpa_su