Add examples for hashed hardcoded passwords from extrausers.bbclass so
that this feature is not hidden away.
Cc: Quentin Schulz <foss+yocto@0leil.net>
(From yocto-docs rev: 5db73c7c5668144ed4629f95378e44f0bd8c8256)
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>