docs: submitting-patches: describe preserving review/test tags

From time to time, the novice kernel contributors do not add Reviewed-by
or Tested-by tags to the next versions of the patches.  Mostly because
they are unaware that responsibility of adding these tags in next
version is on submitter, not maintainer.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

Link: https://lore.kernel.org/r/20201013162725.13572-1-krzk@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>