BB_CURRENT_MC is documented in the Bitbake user manual. Add a reference
to it here.
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
(From yocto-docs rev: a9aaef86bf76027f602546b5d4a3dffc6168d9b4)
Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>