Consistent formatting of term definitions

Suggestion by @TallTed in https://github.com/solid/notifications/pull/196#discussion_r1698791052
> It might be better to convert this segment to a table, with columns of TERM (ordered alphanumerically ascending; possibly re-orderable by other columns and/or ASC/DESC) and DEFINED IN (when linking only to the defining documents) or DEFINED AT (when linking to the fragment IDs of the definitions).