Document how to setup dev environment

Issue Description

Quoting @carsakiller from https://github.com/LuaLS/LuaLS.github.io/pull/35#issuecomment-2134278430:

@sumneko would you be able to provide some more insight into how you develop the language server? I think I recall you saying that development is primarily test-driven. However, I'm not sure how the testing framework works — I believe it is custom? Some pointers on writing and running tests would be appreciated!

Is there a specific flow/method you would recommend for contributors? For the few simple things I have contributed, I have just used print() as described in this PR — but I don't think it would be very efficient for larger changes.

I think creating good documentation here for developing the language server would greatly help the community make some really nice pull requests. I've seen many comments from users eager to help but confused when getting their development environment set up and navigating the codebase.

Some initial work was recently merged in https://github.com/LuaLS/LuaLS.github.io/pull/35.

Additional Notes

No response

Xem lại hướng dẫn phát triển được bổ sung trong LuaLS.github.io pull request 35 và cuộc thảo luận được liên kết để có được ngữ cảnh được yêu cầu. Ghi lại cách thiết lập môi trường, framework kiểm thử và cách viết cũng như chạy các bài kiểm thử, cùng với workflow được khuyến nghị cho các contributor; công việc được xem là hoàn tất khi một người mới có thể làm theo hướng dẫn mà không phải dựa vào việc debug bằng print().