[U-Boot] [PATCH] sandbox: Add an explanation of the sandbox variants

[Simon Glass]

On 18 September 2018 at 17:43, Simon Glass <sjg at chromium.org> wrote:
> There are quite a few builds of sandbox now. Add information about these
> to the README.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
>  board/sandbox/README.sandbox | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)

Applied to u-boot-dm, and now in mainline.