Translations Improvements and add-missings for zh_CN

[inkuxuan]

Hi. Thanks for this fantastic app.

This is a PR for Chinese Simplified translations.

Improves several expressions for "ONLY if sleep mode is enabled" rather than "If enabled". 
Adds several missing translations.

If being credited, would like to show up as "いんく".
Twitter @sayonara_natsu

<3

P.S. I've noticed that there are OyasumiVR Extra Translation Tasks remaining.
Would love to do zh_CN, zh_TW and ja_JP translations.
However I'm not sure where the achievement JSON files are located.

[Raphiiko]

@inkuxuan Thank you for your contribution! ^^

I have updated your PR to add the appropriate credits. Before I merge this however, do you think you could update the credits in README_zh_CN.md (and maybe README_zh_TW.md too?), similar to how it was added to the other readme files? I am not familiar enough with these languages to know how to this properly.

As for the extra translation tasks, feel free to pick them up!

• For the tasks affecting readme files, you can just open a separate PR for them.
• Specifically for the ja_JP readme, I believe なき (our Japanese translator) is currently already working on updating it.
• Achievements (currently) have no JSON file. The exact strings to translate are within the tasks on the board. If you translate them, you can submit them on our Discord Server, by sending me a DM (discord/twitter), or by submitting them in an issue here on GitHub, whichever way you prefer!

[Raphiiko]

Looking good!