doc: update REPL documentation to instantiate the REPL

The documentation currently states that it's not intended to directly
instantiate REPL instances. It is unknown for what reason that's
recommended as it does seem a proper way to handle new REPL instances.

PR-URL: https://github.com/nodejs/node/pull/30928


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>