Update samplesheet in usage

[edmundmiller]

Originally posted by @matthdsm in #132 (comment)

Going to need to address the samplesheets in the docs, and that we only have one example of them. I think we need something that automatically pulls them in for the markdown, so we don't have to edit them in multiple places.

Linked to #138. Probably need a samplesheet overhaul issue at this point 😬