docs/zh_CN: add msi-howto translation

Translate .../PCI/msi-howto.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/d62846e2e820f600c27dc5e49887b3a2892eec17.1639224005.git.siyanteng@loongson.cn


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