docs/zh_CN: typo fix and improve translation

- fix a typo.
- modify some word to improve zh_CN/process/5.Posting.rst.

Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Link: https://lore.kernel.org/r/3adedda2b247be53defc9078104221f00b4c78cd.1632389476.git.siyanteng@loongson.cn


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