doc: add and unify return statements in crypto.md

Conform return statements to the style guide and tool parsers.

Also bring back a description fragment
that seems to be erroneously deleted in
https://github.com/nodejs/node/commit/1e07acd476309e7ddc4981160b89731b61a31179

Backport-PR-URL: https://github.com/nodejs/node/pull/22870
PR-URL: https://github.com/nodejs/node/pull/19853


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>