New committer (doc): Graham Perrin, grahamperrin@

Committer's Guide, steps for new committers, steps 1–4.

Mentors: Glen Barber (gjb) and Sergio Carlavilla (carlavilla).
Approved by: carlavilla.
Pull request: https://github.com/freebsd/freebsd-doc/pull/80
Differential revision: https://reviews.freebsd.org/D35603