The documentation instructs users to add custom fields to the "Custom Fields" or "Additional Fields" field sets in order to get them to render on the VF page.

The documentation also mentions:  “Adding or removing fields affects only those Work Records created after the change” 

So, I made some custom fields, and encountered two problems:
 

1. only 1 of my 5 custom fields showed up on the Field Set setup page. I have checked the field level security, accessibility, everything. No luck.
2. adding the field to the Field Set, and creating a handful of test records did nothing. The field never rendered on the page.