Made tutorial for setting up sumneko-3rd on other text editors

[Deltius5kb]

Thought this might help some other newbies who aren't using vscode.

Currently tutorial specifically talks about neovim but it can easily be expanded to other text editors if other people want to contribute, plus half of it applies to all editors anyway.

[Bilka2]

I would point to the API docs that get shipped with the game instead of suggesting to download them from the website. That way, the docs will definitely be for the same game version as the executable. The vscode extension also gets the json from the game files.

The API docs that get shipped with the game can be found in the doc-html folder in the Application directory.

[Deltius5kb]

Good point, I didn't realise those existed. Done