docs/zh_CN: Add power/index Chinese translation

Translate power/index.rst into Chinese.

Signed-off-by: Tang Yizhou <tangyizhou@huawei.com>
Reviewed-by: Alex Shi <alexs@kernel.org>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Link: https://lore.kernel.org/r/20211229024212.32752-3-tangyizhou@huawei.com


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