sbc8641d: add basic flash setup instructions to README file

...so that I don't have to go work them out from scratch again
by peering at the manual.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

board/sbc8641d/README

@@ -26,3 +26,24 @@ and settings may change with board revisions.
 --------------------
 PCI:
 	The PCI command may hang if no boards are present in either slot.
+
+4. Reflashing U-Boot
+--------------------
+The board has two independent flash devices which can be used for dual
+booting, or for u-boot backup and recovery.  A two pin jumper on the
+three pin JP10 determines which device is attached to /CS0 line.
+
+Assuming one device has a functional u-boot, and the other device has
+a recently installed non-functional image, to perform a recovery from
+that non-functional image goes essentially as follows:
+
+a) power down the board and jumper JP10 to select the functional image.
+b) power on the board and let it get to u-boot prompt.
+c) while on, using static precautions, move JP10 back to the failed image.
+d) use "md fff00000" to confirm you are looking at the failed image
+e) turn off write protect with "prot off all"
+f) get new image, i.e. "tftp 200000 /somepath/u-boot.bin"
+g) erase failed image: "erase FFF00000 FFF3FFFF"
+h) copy in new image: "cp.b 200000 FFF00000 40000"
+i) ensure new image is written: "md fff00000"
+k) power cycle the board and confirm new image works.