rockchip: board: lion_rk3368: update README flash instructions

Add a section to the README on how to flash the on-board eMMC
with the rkdeveloptool.

Signed-off-by: Klaus Goger <klaus.goger@theobroma-systems.com>
Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

board/theobroma-systems/lion_rk3368/README

@@ -26,12 +26,32 @@ Build the full U-Boot and a FIT image including the ATF
 
   > make CROSS_COMPILE=aarch64-unknown-elf- ARCH=arm u-boot.itb
 
-Write to a SD-card
-==================
+Flash the image
+===============
+
+Copy the SPL to offset 32k and the FIT image containing the payloads
+(U-Boot proper, ATF, devicetree) to offset 256k card.
+
+SD-Card
+-------
 
   > dd if=spl-3368.img of=/dev/sdb seek=64
   > dd if=u-boot.itb of=/dev/sdb seek=512
 
+eMMC
+----
+
+rkdeveloptool allows to flash the on-board eMMC via the USB OTG interface with
+help of the Rockchip loader binary.
+
+  > git clone https://github.com/rockchip-linux/rkdeveloptool
+  > cd rkdeveloptool
+  > autoreconf -i && && ./configure && make
+  > git clone https://github.com/rockchip-linux/rkbin.git
+  > ./rkdeveloptool db rkbin/rk33/rk3368_loader_v2.00.256.bin
+  > ./rkdeveloptool wl 64 ../spl.img
+  > ./rkdeveloptool wl 512 ../u-boot.itb
+
 
 If everything went according to plan, you should see the following
 output on UART0: