brainstorm best way to document what this library offers

[fnrizzi]

we need to port the relevant doc from https://github.com/Pressio/pressio/tree/develop/docs

but before we do that, we need to brainstorm a bit about what is the best way to document what this pressio-ops does.

for example, say that we need to document the pressio::ops::product, how do we best explain it? via a table? just a description?