docs: maintainer: discourage taking conversations off-list

Multiple vendors seem to prefer taking discussions off list, and
ask contributors to work with them privately rather than just send
patches to the list. I'd imagine this is because it's hard to fit in
time for random developers popping up with features to review into
packed schedule. From what I've seen "work in private" usually means
someone on the company side will be assigned to handle the interaction,
possibly months later. In worst case, the person scheduled to help
the contributor takes over and writes the code themselves.
This is not how the community is supposed to work.

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240713235020.820910-1-kuba@kernel.org
Link: https://lore.kernel.org/r/20240712144903.392284-1-kuba@kernel.org