docs/zh_CN: Add sched-nice-design Chinese translation

Translate scheduler/sched-nice-design.rst into Chinese.

Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/20220312072642.23118-1-tangyizhou@huawei.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>