[WIP, help appreciated] Add Vietnamese translation (vi-VN)

[KTrain5169]

I accidentally closed the old pull request, so here it is again.

• [x] README.md
• [ ] credits.md
• [ ] users.md (in progress)
• [ ] tech.md
• [ ] timeline.md
• [ ] 2023-06-08-meeting.md
• [ ] stages.png
• [ ] flowchart.png
• [ ] sandboxfile.png
• [ ] localappdata.png
• [x] unhide.mp4

The items marked in bold are the ones I need extra help on (you will notice they are PNGs, that's because I'm not good at image editing)

[KTrain5169]

I don't know how to use the checklist feature on GitHub, so if someone could tell me how to mark items as completed, that'd be great!