Updated and improved MODDING.md

[Inglonias]

Summary

SUMMARY: None

Purpose of change

Update our modding documentation to make it easier to get started with writing mods.

Describe the solution

It was suggested that someone update the documentation for modding the game, and so I took it upon myself to do this.

Describe alternatives you've considered

Not really an alternative so much as some concerns I have with what I wrote. It turns out that after LUA support was dropped, some new code was written more or less so that the No Zombie Revival mod could exist without it (among a few other mods). Because that mod is currently at risk of going away, I felt it necessary to put that mod at the back of this document. If someone here understands how that "monster_adjustment" structure actually works, please add it to the JSON_INFO.md file.

Testing

N/A. Documentation

Additional context

I consider this to be a first draft. Feel free to recommend anything you think is missing from this document to be added. It would also be helpful if you added links for research I can do on whatever you want me to add, even if it's just a link to the right section of the