Explain parent-child court relationships in documentation

[mlissner]

I think there are two parts to this:

1. We need to add something to the API about how parent-child court relationships work.

2. We need to document in the search API that we use a trick to select child courts for certain courts.

@flooie do you think you could help with this one?

[mlissner]

Just posted this answer to a client with questions about this:

[mlissner]

@flooie, can you please put this on a backlog so we know when it will be completed?