Note on the relations page that views don't have relations by default
We need a PR to https://postgraphile.org/postgraphile/next/relations pointing to the views page and noting that we automatically support relationships via foreign key constraints on tables, and that views do not have foreign key constraints and thus do not get automatic relationships (but that you can add them via the `@foreignKey` smart tag).

See discussion in https://github.com/graphile/crystal/issues/2331