docs/zh_CN: Improve zh_CN/process/5.Posting.rst

Improve language and grammar of zh_CN/process/5.Posting.rst

Signed-off-by: Wu XiangCheng <bobwxc@email.cn>
Reviewed-by: Alex Shi <alex.shi@linux.alibaba.com>
Link: https://lore.kernel.org/r/e2e8e109c7709ebbed9f536cbe49f6f56f38d5bf.1614920267.git.bobwxc@email.cn


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