docs: submitting-patches: document the format for affiliation

docs: submitting-patches: document the format for affiliation

Adding company name in round brackets to From/SoB lines
is fairly common, but I don't see it documented anywhere.
Every now and then people try to add the sponsorship lines
to the commit message, fun example from this merge window:

  Sponsored by:   The FreeBSD Foundation

from commit 2ce67f8bf1ce ("wifi: iwlwifi: mvm: fix iwl_ssid_exist()
check"). Better format would be:

  Author: Miri Korenblit (FreeBSD Foundation) <...

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20250203174626.1131225-1-kuba@kernel.org