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

查看 LuaLS.github.io pull request 35 中新增的开发指南以及链接的讨论，以了解所需的背景信息。记录环境设置、测试框架、如何编写和运行测试，以及推荐贡献者采用的工作流程；完成的标准是新贡献者无需依赖使用 print() 进行调试即可按照指南操作。