doc: update buffer examples

Move the print statements below a console.log call.

PR-URL: https://github.com/nodejs/node/pull/18758


Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>