docs/zh_CN: add a man-pages link to zh_CN/index.rst

update to commit 48987606

 ("docs: add a man-pages link to the front
page")

Signed-off-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Link: https://lore.kernel.org/r/6e289528ed1b40c1fcc03ea5e854e7c8ba264e67.1665467392.git.bobwxc@email.cn
Signed-off-by: Jonathan Corbet <corbet@lwn.net>