doc: properly inheriting from EventEmitter

There are so many buggy code out there, just because not inheriting
properly from `EventEmitter`. This patch gives an official
recommendation.

PR-URL: https://github.com/nodejs/io.js/pull/2168


Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>