docs/zh_CN: add scheduler sched-bwc translation

Translate .../scheduler/sched-bwc.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/e5f96f741012af6d4c4a27e7d1aab076ddffd322.1638517064.git.siyanteng@loongson.cn


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