docs/zh_CN: add vm/index translation

Translate ../vm/index.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Tang Yizhou <tangyizhou@huawei.com>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/60c579b34792c4c76194c4843a695263a982b37d.1641866889.git.siyanteng@loongson.cn


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