🚀 The feature

I have added vietnamese vocabs for VNese devs like me to use doctr better, following this issue: #464 (review)
This is my pull request, please review it.

Motivation, pitch

I am very appreciate and congrats on your great work. This package will help me alot in my work :) However, I am working on Vietnamese OCR, so Vietnamese vocabs is required and I can't see any guide to locally added vietnamese vocabs without changing the main repository (which I am quite afraid of damaging something I dont know). It would be very nice if you could guide me or review my contribution on vietnamese vocabs here: #878

Alternatives

No response

Additional context

And please, if you agree with my contribution, can you also give me soem tips on how to apply the new vocab in your work ? Are there any tools or guide line on how to create and train a custom dataset ?
Thank you very much ~!