Refine Simplified Chinese Translations and Add Translations for documents in Simplified Chinese.

[Blealtan]

PR Checklist

• The commit message follows our guidelines.\

  What are the guidelines on commit message? I can't access the documentation site currently.

• Tests for the changes have been added (for bug fixes / features).
  • Muse | Mist have been tested.
  • Pisces | Gemini have been tested.
• Docs have been added / updated (for bug fixes / features).

PR Type

• Bugfix.
• Feature.
• Code style update (formatting, local variables).
• Refactoring (no functional changes, no api changes).
• Build related changes.
• CI related changes.
• Documentation content changes.
• Other... Please describe:

What is the current behavior?

• post/totalcount and post/totaltime in languages/zh-Hans.yml are not translated.
• Documentations under docs/cn are not translated.

Issue Number(s): N/A

What is the new behavior?

• Untranslated words in zh-Hans are now translated.

• Translations for documentations, including DATA-FILES.md, INSTALLATION.md and README.md, are finished.

• Screens with this changes: N/A

• Link to demo site with this changes: N/A

How to use?

N/A.

Does this PR introduce a breaking change?

• Yes.
• No.

[ivan-nginx]

Cool and thank u!
But need to wait a moment: i write additional docs right now, so, can u wait a little and then do full translate of new files?

[Blealtan]

Yeah of course. I'll wait for further updates and translate them.

[ivan-nginx]

It's ready. This commit: 3eebd5f

[ivan-nginx]

Fixed, this commit: 3fbb715

[Blealtan]

INSTALLATION.md is updated and translation for UPDATE-FROM-5.1.x.md is added. In the translation of the latter one I made some style changes as for Markdown best practices. You may want check it before accepting.

[ivan-nginx]

Cool dude! Thank's a lot! 👍