Add translation zh_CN/admin-guide/numastat.rst and link it to
zh_CN/admin-guide/index.rst while clean its todo entry.

commit 77691ee9 ("Documentation: update numastat explanation")
Signed-off-by: Tao Zou <wodemia@linux.alibaba.com>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/tencent_AB1A2D84652D748A2290F5305B94D4612307@qq.com