docs/zh_CN: add vm hugetlbfs_reserv translation

Translate .../vm/hugetlbfs_reserv.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>