board/avnet/zedboard/: improve readme.txt explanations

[Thomas: fix small grammar issue noticed by Spenser Gilliland, adjust
commit title.]

Signed-off-by: Javier Domingo Cansino <javierdo1@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

board/avnet/zedboard/readme.txt

@@ -5,26 +5,68 @@ System-On-Chip.
 Zedboard information including schematics, reference designs, and manuals are
 available from http://www.zedboard.org .
 
-To boot the Zedboard using a buildroot generated image copy the following files
-to the sdcard:
-	zynq-zed.dtb -> devicetree.dtb
-	rootfs.cpio.gz.uboot -> uramdisk.image.gz
-	uImage -> uImage
-	boot.bin -> boot.bin
+The U-Boot firmware for the Xilinx Zynq All Programmable SoC depends
+on some propietary code. This dependency consists of a pair of
+files are available from the Xilinx SDK installation.
 
-U-Boot SPL Support
--------------
+You will need these files from Xilinx SDK installation to generate
+the U-Boot firmware:
+	ps7_init.c
+	ps7_init.h
+
+Buildroot will create the following files and place them in the
+<output>/images directory.
+	zynq-zed.dtb
+	rootfs.cpio.uboot
+	uImage
+	u-boot.img
+	boot.bin
+
+
+uboot.bin  -- U-Boot SPL w/ Xilinx boot.bin wrapper
+---------------------------------------------------
 
 Due to licensing issues, the files ps7_init.c/h are not able to be
 distributed with the U-Boot source code.  These files are required to make a
 boot.bin file.
 
-If you already have the Xilinx tools installed, the follwing sequence will
+If you already have the Xilinx tools installed, the following sequence will
 unpack, patch and build the rfs, kernel, uboot, and uboot-spl.
 
 make zedboard_defconfig
 make uboot-patch
 cp ${XILINX}/ISE_DS/EDK/sw/lib/hwplatform_templates/zed_hw_platform/ps7_init.{c,h} \
-output/build/uboot-xilinx-v2014.1/boards/xilinx/zynq/
+output/build/uboot-xilinx-v2014.1/board/xilinx/zynq/
+
+After copying these files into the U-Boot source tree, you can
+continue the build with:
+
 make
 
+*Notice*
+While the build will successfully complete without the ps7_init.*
+files,  the uboot.bin file generated by this configuration will not
+function properly on the Zedboard.  Therefore, it is imperative that
+the ps7_init.* files be copied into the U-Boot source tree any time
+the clean, or uboot-dirclean targets are made.
+
+
+Resulting system
+----------------
+A FAT32 partition should be created at the beggining of the SD Card
+and the following files should be installed:
+	/boot.bin
+	/devicetree.dtb
+	/uImage
+	/uramdisk.image.gz
+	/u-boot.img
+
+
+All needed files can be taken from output/images/
+
+boot.bin, uImage and u-boot.img are direct copies of the same files
+available on output/images/
+
+devicetree.dtb is just zynq-zed.dtb renamed.
+
+uramdisk.image.gz is rootfs.cpio.uboot renamed