Docs: Clarify `useSelectedLayoutSegments` returns "children" in parallel routes

### What is the documentation issue? The documentation for `useSelectedLayoutSegments` does not mention that when used with parallel routes, the returned array starts with `"children"` to represent the default branch inside the slot. For example, if you navigate to `@header/bar`, the hook returns: `["children", "bar"]` but the docs imply it would simply return: `["bar"]` This is confusing and not explained anywhere in the parallel routes or API reference pages. ### Is there any context that might help us understand? ``` app/ └── example5/ ├── @header/ │ └── \[segment]/ │ └── page.tsx └── layout.tsx ```` My code in `example5/layout.tsx`: ```tsx "use client"; import { useSelectedLayoutSegments } from "next/navigation"; export default function Example5Layout({ children }) { const headerSegments = useSelectedLayoutSegments("header"); return ( <div> <p>Header segments: {JSON.stringify(headerSegments)}</p> {children} </div> ); } ```` When I visit `/example5/bar`, I see in the browser console or UI: ``` Header segments: ["children", "bar"] ``` ### Does the docs page already exist? Please link to it. https://nextjs.org/docs/13/app/building-your-application/routing/parallel-routes#useselectedlayoutsegments