Fields are missing info on how to update them programmatically

[manuelmoreale]

Issue with Reference
The other day I was programmatically updating content on a site and ended up asking on the forum how to solve a silly issue. https://forum.getkirby.com/t/programmatically-updated-a-files-field/27918

What I realised is that there's no documentation, as far as i'm aware, on how to programmatically update all the different types of fields.

It would be useful to have documented what kind of value each field is expecting when doing things programmatically.

Expected
A simple description of what kind of value Kirby wants me to pass to the various update() functions when working with a specific field type.