guide Howto guide: avoid mod conflicts

[Nightinggale]

We start to get mod conflicts and since there are ways to code, which are prone to conflicts and ways to code, which tend to avoid conflicts, I decided to write a guide on some concepts, which can be useful to avoid issues with other mods or future ONI updates.

Since we (to my knowledge) still haven't got a good shared wiki for modding, I decided to add the page on my personal wiki. It can always be moved later.