docs/howto: Replace abundoned URL of gmane.org

docs/howto: Replace abundoned URL of gmane.org

Somehow, there remains a link to gmane.org, which stopped working
in 2016, in howto.rst. Replace it with the one at lore.kernel.org.
Do the same changes under translations/ as well.

Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Cc: Federico Vaga <federico.vaga@vaga.pv.it>
Cc: Alex Shi <alexs@kernel.org>
Cc: Yanteng Si <siyanteng@loongson.cn>
Cc: Hu Haowen <src.res@email.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/20220930021936.26238-1-akiyks@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>