When reading Kconfig help messages to understand ENV_OFFSET and
ENV_OFFSET_REDUND, developers may not realise that they need to also
look at the chosen ENV_IS_IN_* options to see how the offsets will be
interpreted.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Simon Glass <sjg@chromium.org>