doc/zh_CN: add Chinese document coding style reminder

doc/zh_CN: add Chinese document coding style reminder

The coding style requirement for Chinese document is easy to be overlooked.
Add the request as a remdiner.

Signed-off-by: Alex Shi <alexs@kernel.org>
Cc: Yanteng Si <siyanteng01@gmail.com>
Cc: Tang Yizhou <tangyizhou@huawei.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Link: https://lore.kernel.org/r/20211209095604.68954-1-alexs@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>