Add prominent "Next" links to selected docs pages

## Why are we implementing it? (sales eng)

It's not always clear which sections are good further reading on a topic. Without guidance people may feel lost after arriving on a docs page from a google search.

## Communication goals (e.g. detailed howto vs orientation)

Choose a (small!) collection of links for further reading for popular pages. Ideally just one link? Add it as a big call-to-action at the bottom of each page. Should we remove the auto-generated "next" button generated by sphinx on each page?

It makes sense to think about this issue after finishing #606 since that will affect the positioning of items in general.