add descriptions to parent and child fields to explain how they work

[joachim-n]

Service landing pages and service sub-landing pages have parent and child fields.

It's not clear from the forms that you're supposed to use these to form a 2-way relationship (see #196 for instance), or what happens when you set something in those fields.

AFAICT,

• the child field makes the child appear as an item on the page
• the parent field controls the breadcrumb
• there might be other effects I'm not aware of.

[tonypaulbarker]

@joachim-n I think that's the gist of it. Parent is for structure (let's check what we get out of the box - is it paths and breadcrumbs?). The child field is for linking to the child page (link and description).

I think it's a good thing to have both because it's useful to have some control over the display of those links.

• there might be other effects I'm not aware of.
  We can check and get review of it. The main one I can think of is customisations - people can alter things like display, structure, breadcrumbs and paths.

In the first instance, I think it's worth checking the accuracy of https://docs.localgovdrupal.org/content/features/services.html and updating that as necessary.

[stephen-cox]

Would make sense to have some documentation on the docs site for how the parent <-> child relation works, but we could also make it clearer what the unused links on a sub-landing page are:

[stephen-cox]

Not clear that's it possible to drag and drop to items in the pages linking here, so could definitely do with some UX improvments