doc: add example for zlib.createGzip()

PR-URL: https://github.com/nodejs/node/pull/28136


Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Masashi Hirano <shisama07@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>