docs/zh_CN: add scheduler index translation

Translate .../scheduler/index.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/e015c61f64fc0d4d3a49f0e85e925f00df433721.1638777809.git.siyanteng@loongson.cn


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