Update package examples for scope and link to categories on the package listing page

[lwasser]

Is there a way we can make these example sections more up to date? Maybe a page on the pyopensci website filtering by category?

Originally posted by @coatless in #359 (comment)

[lwasser]

The challenge with implementing this is that currently we use a front end filter approach. It might be that we can figure out a way to do it that would support a backend or front end + link option. We just need to think about how we'd engineer that into our website.