Update the pinned channel in `md-to-db`, which bumps the Pandoc version, which fixes https://github.com/NixOS/nixpkgs/issues/125511 maybe.
mkOrder
Add a section on ordering option definitions. Also mention `mkDefault` in the section on `mkOverride`. Clarify the code a bit by renaming `defaultPriority` to `defaultOverridePriority` and introducing `defaultOrderPriority`.