sheevaplug: add a basic readme

Describing how to update the board.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/sheevaplug/readme.txt

@@ -0,0 +1,36 @@
+Sheevaplug
+==========
+
+Once the build process is finished you will have the following files
+in the output/images/ directory:
+
+- u-boot.kwb
+- uImage.kirkwood-sheevaplug
+- rootfs.jffs2
+
+Copy these to a TFTP server, connect ethernet and mini-USB cable and
+power up the board. Stop the board in U-Boot and update U-Boot by
+executing:
+
+setenv serverip <ipaddress-of-tftp-server>
+setenv bootfile <path/to/u-boot.kwb>
+bootp
+nand erase 0x0 0x80000
+nand write $fileaddr 0x0 0x80000
+reset
+
+Once the new U-Boot boots up, stop it again and update Linux kernel
+and rootfs by:
+
+setenv serverip <ipaddress-of-tftp-server>
+setenv bootfile <path/to/uImage.kirkwood-sheevaplug>
+bootp
+nand erase.part kernel
+nand write $fileaddr kernel 0x400000
+
+setenv bootfile <path/to/rootfs.jffs2>
+bootp
+nand erase.part rootfs
+nand write $fileaddr rootfs $filesize
+
+reset