docs/zh_CN: Add rust index Chinese translation

Translate .../rust/index.rst into Chinese.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Wu XiangCheng <bobwxc@email.cn>
Link: https://lore.kernel.org/r/74e20d998bc2825d770c8b4d954e42b0d613ec09.1666959529.git.siyanteng@loongson.cn


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