epjitsu: document how to extract .nal files in Linux

In Fujitsu ScanSnap installation DVDs the .nal firmware files required
for the epjitsu backend to work are located in cabinet files.

The script snippet locates these cabinet files on the DVD and extracts all
.nal files it finds.

backend/epjitsu.conf.in

@@ -17,6 +17,35 @@
 # find them. They should be ~65K, and have the scanner's name as part of the
 # file name. They are often inside a .cab file.
 
+# To extract .nal files from cabinet files on Linux, use the following steps:
+# (you need the "unshield" tool, which is - in Debian - in the unshield package)
+#
+#  1) Mount the ScanSnap installation DVD
+#     (mount point e.g. /media/dvd)
+#
+#  2) Extract the .nal files c$ from the cabinet files on the DVD
+#     using the following shell script:
+#
+#	# loop over all cabinet files found on the DVD
+#	for cab in $(find /media/dvd/ -name \*.cab); do
+#	    # search for .nal files in the cabinet files
+#	    nalinfo=$(unshield l $cab | grep '\.nal$')
+#
+#	    # we found something
+#	    if [ -n "$nalinfo" ]; then
+#	        #echo -e "=== $cab ===\n$nalinfo"
+#
+#	        # loop over all fields in $nalinfo
+#	        for nal in $nalinfo; do
+#	            # if the element of $nalinfo is a .nal file name
+#	            if echo "$nal" | grep -q '\.nal$' - 2>/dev/null; then
+#	                # extract .nal file form the cabinet file
+#	                unshield x "$cab" "${nal##*\\}"
+#	            fi
+#	        done
+#	    fi
+#	done
+
 # Copy the file someplace sane can reach it. Then update the line below.
 # NOTE: the firmware line must occur BEFORE the usb line for your scanner