Docs: add walk-through examples of how to use Zookeeper concepts in experiments

[leonoverweel]

I think maybe it'd be good to have some simple examples of how these Zookeeper concepts (Fields, @components, and ComponentFields) can/should be used in the context of an experiment/@task, perhaps alongside or replacing the more abstract child/parent examples we have in README.md now. I've still learned this mostly from pattern matching what I've seen others do across Zoo and other places. It'd be nice to have a reference of the most Pythonic Zookeperic ways of doing different things.

(From #134.)