doc: put information about the past in details tags

To make the README more scannable and keep it manageable in length, put
emeriti and past keys lists in details tags.

PR-URL: https://github.com/nodejs/node/pull/39321


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>