add a global `.luacheckrc`

[BuckarooBanzay]

i wanted to add a luacheck-workflow + .luacheckrc to the modpack but realized somewhere in the end that there were already some .luacheckrc files in the mod-folders itself :facepalm:

Just placing this here until:

• Someone wants to convert all rc-files to one, or
• Someone adds a proper luacheck-workflow for the various mod-folders

[BuckarooBanzay]

closing this in favor of #28