docs: add examples and crate docs

[onbjerg]

Adds some missing docs and some examples in the top-level module documentation. I am not entirely sure on what an "instance" is, so I did not explain much in the docs for that - is it a value?

[ralexstokes]

"instance" is, so I did not explain much in the docs for that - is it a value?

yeah, "instance" is just an instance of the type, aka a value -- if you want to change the name feel free