plan9.ini(8): document iwl options

sys/man/8/plan9.ini

@@ -381,6 +381,29 @@ programming interface.
 Currently the only tested cards are those based on the
 Intersil Prism 2.5 chipset.
 .
+.TP
+.B iwl
+Intel Wireless WiFi Link mini PCI-Express adapters require
+firmware from
+.B http://firmware.openbsd.org/firmware/
+to be present on attach in
+.B /lib/firmware
+or
+.B /boot.
+To select the access point, the
+.B essid=
+parameter can be specified at boot or set during runtime
+like:
+.EX
+	echo essid left-armpit >/net/ether1/clone
+.EE
+Scan results appear in the
+.B ifstats
+file and can be read out like:
+.EX
+	cat /net/ether1/ifstats
+.EE
+Ad-hoc mode or encryption is currently not supported.
 .SS DISKS, TAPES
 (S)ATA controllers are autodetected.
 .SS \fL*nodma=\fP