Make relation documentation clearer

I've struggled a little getting started with this framework, especially when it comes to documentation of the relation fields.

In [https://orchid.software/en/docs/field/#relation](the docs), relations are mentioned as standalone, like this.

Relation::make('idea')
    ->fromModel(Idea::class, 'name')
    ->title('Choose your idea');

For me, this will leave an empty relation field that fails silently.
I've since learned that in my projects, I have to do something like this:

Relation::make('user.idea')
    ->fromModel(Idea::class, 'name')
    ->title('Choose your idea');

Since the relation appears on a page belonging to another model.
I don't mind adding a PR with a suggestion for how to reflect this in the docs but wanted to gather feedback beforehand, as I don't have a lot of experience contributing to public repos.

Start at the relation-field documentation linked in the issue and compare the standalone example with the nested user.idea example. Clarify the reported distinction in the documentation, with the work complete when users can understand why the standalone example produces an empty relation field in this case.