wd719x: Add firmware documentation

Add documentation and script to obtain required firmware.
Signed-off-by: NOndrej Zary <linux@rainbow-software.org>
Reviewed-by: NHannes Reinecke <hare@suse.de>
Signed-off-by: NChristoph Hellwig <hch@lst.de>

Documentation/scsi/wd719x.txt

+Driver for Western Digital WD7193, WD7197 and WD7296 SCSI cards
+---------------------------------------------------------------
+
+The card requires firmware that can be cut out of the Windows NT driver that
+can be downloaded from WD at:
+http://support.wdc.com/product/download.asp?groupid=801&sid=27&lang=en
+
+There is no license anywhere in the file or on the page - so the firmware
+probably cannot be added to linux-firmware.
+
+This script downloads and extracts the firmware, creating wd719x-risc.bin and
+d719x-wcs.bin files. Put them in /lib/firmware/.
+
+#!/bin/sh
+wget http://support.wdc.com/download/archive/pciscsi.exe
+lha xi pciscsi.exe pci-scsi.exe
+lha xi pci-scsi.exe nt/wd7296a.sys
+rm pci-scsi.exe
+dd if=wd7296a.sys of=wd719x-risc.bin bs=1 skip=5760 count=14336
+dd if=wd7296a.sys of=wd719x-wcs.bin bs=1 skip=20096 count=514
+rm wd7296a.sys