message: core-api: document createRouteRef type inference logic
diff: @@ -47,7 +47,12 @@ export class AbsoluteRouteRef<Params extends { [param in string]: string }> {
  }
  export function createRouteRef<
  + // Params is the type that we care about and the one to be embedded in the route ref.
  + // For example, given the params ['name', 'kind'], Params will be {name: string, kind: string}
  Params extends { [param in ParamKey]: string },
  + // ParamKey is here to make sure the Params type properly has its keys narrowed down
  + // to only the elements of params. Defaulting to never makes sure we end up with
  + // Param = {} if the params array is empty.
  ParamKey extends string = never
  >(config: {
  params?: ParamKey[];
  