Write documentation describing how to configure a butler, including:
- how configuration options are inherited and how that can be changed (i.e. search paths)
- what options are available at the top level, and where to find documentation on registry- and datastore-specific options.
One challenge is figuring out where to put the source of truth. We'd like the docs to be on pipelines.lsst.io, certainly, but it'd also be nice to put them next to the code that defines them, and right now that definition is completely implicit.