MAINTAINERS: Become the docs/zh_CN maintainer

It's time to become a maintainer of Chinese documentation, and Yanteng's plan
is to help everyone with the utmost enthusiasm and patience.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/b0c1324d1d63846d700ab354446a6deaf30754c0.1652712771.git.siyanteng@loongson.cn


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