Document querying using keyless entities with relationships/navigation properties

Reading the documentation it wasn't very clear to me what kind of scenarios Navigation with Query Types are supported.

@julielerman raised this issue [here](https://github.com/aspnet/EntityFrameworkCore/issues/11971), and a few annotations have been made to the documentation ([here](https://github.com/aspnet/EntityFramework.Docs/pull/698/files)) but I don't think this is clear enough.

We could have a sample showing the "right way" of doing it: with the "inverse" navigation property, and a sample showing what would happen if you do it the other way, maybe showing the exception you would get, so people can find the issue quicker when searching.

What do you think? I could write a concise sample with the entities used in the docs showing this more clearly.