Headless Raspberry Pi Setup
Don’t have an extra keyboard or HDMI cable? Here’s how to do a headless Raspbian install on your Pi.
To use headless wireless, edit wpa_supplicant.conf in the boot partition (direct from Windows):
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
ssid="YOUR SSID HERE"
psk="YOUR PASSWORD HERE"
}
(taken from Raspberry Pi 3 Raspbian Jessie with WiFi, SSH, Headless Setup with No Keyboard or Ethernet step 5, also see first comment by Bernhard Reinel)