[U-Boot] [PATCH v2] README.kconfig: document backward compatibility "make *_config"

[Stephen Warren]

On 08/27/2014 07:56 PM, Masahiro Yamada wrote:
> Commit 3ff291f371fa9858426774f3732924bacb61ed1c
> (kconfig: convert Kconfig helper script into a shell script)
> restored "<board>_config" target for backward compatibility.
> It should be documented.

Reviewed-by: Stephen Warren <swarren at nvidia.com>