Documentation/contributing: Add sign-off procedure

Currently, this only exists on the old wiki and the developers.html page
on coreboot.org, but it really ought to be somewhere in the new docs
alongside the other contribution guidelines. This was largely copied
from the text from the developers.html page.

Change-Id: If50b3827ab36234719f9a90239caec4612eb6762
Signed-off-by: Nicholas Chin <nic.c3.14@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/74825
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>

0 files changed, 0 insertions, 0 deletions