Add rules around voting

This is the next chapter of our ways of working, detailing how we are to vote. It is surprisingly difficult to make this precise -- in the end, we punted on some of this precision, as you will see in the preamble. Instead, we focused on delineating exactly what comprises a vote, in order to make decision-making unambiguous.

Co-authored with @copton and @trac-ryantrinkle.

All feedback welcome.