[IMP] doc: Add example for `inherit_id` + `mode`

Added an example because it's non-trivial to realize why you would want
to set `mode` to `primary` together with `inherit_id`.

Another way to look at it is that the view matching doesn't understand
delegation inheritance. If it did there would be no need to override
`mode` because it would be able to see that the parent and derived views
refer to related models. But since that feature might not be worth the
effort, it's ok for me to just document the current situation.