warpboard: README: Improve instructions about using wifi

Provide a more complete set of instructions on how to get Wifi
working on the warpboard.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/freescale/warpboard/README

@@ -66,4 +66,14 @@ $ hciconfig hci0 up
 Using Wifi
 ==========
 
-$ ifconfig wlan0 up
+Enable the wireless_utils and wpa_suplicant packages, and then run:
+
+# modprobe brcmfmac
+# iwconfig wlan0 essid ACCESSPOINTNAME
+# wpa_passphrase ACCESSPOINTNAME > /etc/wpa.conf
+(enter the wifi password and press enter)
+# wpa_supplicant -Dwext -iwlan0 -c /etc/wpa.conf &
+# udhcpc -i wlan0
+# ping buildroot.org
+
+Enjoy!