Create a separate section for the volunteer team

The volunteer team will be referred to in other places in the document,
so is moved into its own section.
Add a 3rd option for suggesting changes

Lower the barrier to entry for making changes to the document by
suggesting that the reader contacts Murray or one of the volunteer team
privately.
Clarify the provenance of the document

Mention that Tom and Aanand were co-authors of the original draft, and
link to the github contributors page.
Move information on joining the volunteer team

The information on how to join the volunteer team makes more sense in
the volunteer team section.