doc: add simple example to rename function

Added a simple example showing how to rename
a file.

Refs: https://github.com/nodejs/node/issues11135

PR-URL: https://github.com/nodejs/node/pull/18812


Reviewed-By: Matheus Marchini <matheus@sthima.com>
Reviewed-By: Tiancheng "Timothy" Gu <timothygu99@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>