arm: mvebu: clearfog: document boot from UART

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Stefan Roese <sr@denx.de>

board/solidrun/clearfog/README

@@ -16,3 +16,23 @@ $ sudo dd if=u-boot-spl.kwb of=/dev/sdX bs=512 seek=1
 
 Please use the correct device node for your setup instead
 of "/dev/sdX" here!
+
+Boot from UART:
+---------------
+
+Connect the on-board micro-USB (CF Pro: CON11, CF Base: CON5)
+to your host.
+
+Set the SW1 DIP switches to UART boot (0: OFF, 1: ON):
+
+  ClearFog Base: 01001
+  ClearFog Pro:  11110
+
+Run the following command to initiate U-Boot download:
+
+  ./tools/kwboot -b u-boot-spl.kwb /dev/ttyUSBX
+
+Use the correct UART device node for /dev/ttyUSBX.
+
+When download finishes start your favorite terminal emulator
+on /dev/ttyUSBX.