doc: add @othiym23 to list of collaborators

Forrest Norvell (that's me!) has been a collaborator since roughly April
2015. I thought I'd added myself to the list of collaborators, but
apparently hadn't. I was onboarded by @chrisdickinson as part of the
second or third group of collaborators added to the project.

PR-URL: https://github.com/nodejs/node/pull/6945


Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>