docs/zh_CN: Add translation zh_CN/doc-guide/contributing.rst

Add new translation
  Documentation/translations/zh_CN/doc-guide/contributing.rst

Signed-off-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Reviewed-by: Alex Shi <alexs@kernel.org>
Link: https://lore.kernel.org/r/3c48979277abe63d1d157c7eb9187d32380db42a.1618295149.git.bobwxc@email.cn


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