cosmetic: Better explain how to use the kirkwood kwbimage.cfg file.

Hi,

This adds to the documenation to explain how to use the
kwbimage.cfg file necessary to generate an image with
prefixed board setup values necessary for the kirkwood
boards.

Signed-off-by: Karl O. Pinc <kop@meme.com>

doc/README.kwbimage

@@ -25,13 +25,24 @@ for ex.
 		-T kwbimage -a 0x00600000 -e 0x00600000 \
 		-d u-boot.bin u-boot.kwb
 
+
 kwbimage support available with mkimage utility will generate kirkwood boot
-image that can be flashed on the board NAND/SPI flash
+image that can be flashed on the board NAND/SPI flash.  The make target
+which uses mkimage to produce such an image is "u-boot.kwb".  For example:
+
+  export BUILD_DIR=/tmp/build
+  make distclean
+  make yourboard_config
+  make $BUILD_DIR/u-boot.kwb
+
 
 Board specific configuration file specifications:
 ------------------------------------------------
-1. This file must present in the $(BOARDDIR) and the name should be
-	kwbimage.cfg (since this is used in Makefile)
+1. This file must present in the $(BOARDDIR).  The default name is
+	kwbimage.cfg.  The name can be set as part of the full path
+        to the file using CONFIG_SYS_KWD_CONFIG (probably in
+        include/configs/<yourboard>.h).   The path should look like:
+        $(SRCTREE)/$(CONFIG_BOARDDIR)/<yourkwbimagename>.cfg
 2. This file can have empty lines and lines starting with "#" as first
 	character to put comments
 3. This file can have configuration command lines as mentioned below,