added most of the chinese translations

[DetectiveKarenthy]

Description

Added most of the Chinese Simplified translations. Some of the text are not used anymore in json file and therefore not translated.

Motivation and Context

The Chinese Simplified language is not present yet.

How Has This Been Tested?

No change of any functional code, only the language is added.

Checklist:

• Some of the strings are hardcoded in the HTML file, those are not and cannot be translated.
• Some strings are obsolete in json file (not used anywhere). Please purge the json file and then I can continue translation.

[bobdos]

• please add both of index.html and guide.html as well;
• please change cn.json to zh-cn.json;
• will add more comments soon.

thanks for your effort.

[DetectiveKarenthy]

@bobdos @valentcheung Thanks for the comments. I've updated accordingly.

[langerhans]

Is this ready for review now?

[DetectiveKarenthy]

@langerhans From my side it is ready. Again not all entries are translated in the JSON file as they do not appear anywhere on the website. Existing comments have been resolved.