warp: Add a README file

Provide instructions on how to upgrade U-boot in the eMMC.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>

board/warp/README

+How to Update U-boot on Warp board
+----------------------------------
+
+Required software on the host PC:
+
+- imx_usb_loader: https://github.com/boundarydevices/imx_usb_loader
+
+- dfu-util: http://dfu-util.sourceforge.net/releases/
+
+Build U-boot for Warp:
+
+$ make mrproper
+$ make warp_config
+$ make
+
+This will generate the U-boot binary called u-boot.imx.
+
+Put warp board in USB download mode
+
+Connect a USB to serial adapter between the host PC and warp
+
+Connect a USB cable between the OTG warp port and the host PC
+
+Open a terminal program such as minicom
+
+Copy u-boot.imx to the imx_usb_loader folder.
+
+Load u-boot.imx via USB:
+
+$ sudo ./imx_usb u-boot.imx
+
+Then U-boot should start and its messages will appear in the console program.
+
+Use the default environment variables:
+
+=> env default -f -a
+=> save
+
+Run the DFU command:
+=> dfu 0 mmc 0
+
+Transfer u-boot.imx that will be flashed into the eMMC:
+
+$ sudo dfu-util -D u-boot.imx -a boot
+
+Then on the U-boot prompt the following message should be seen after a succesful
+upgrade:
+
+#DOWNLOAD ... OK
+Ctrl+C to exit ...
+
+Remove power from the warp board.
+
+Put warp board into normal boot mode
+
+Power up the board and the new updated U-boot should boot from eMMC