Document how to send emails

[RealOrangeOne]

The current process involves PRs against either https://github.com/srobo/volunteer-emails/ or https://github.com/srobo/team-emails, which is somewhat widespread understood, but beyond that is mostly unknown.

Specifically, how to send emails to volunteers (Mailchimp), competing team leaders (Google Group), and the year-agnostic team leaders (Mailchimp)

This should intentionally not document how to use the services, but more how we use them. It should cover the whole flow, from which repo, to asking for review, to the actual sending process, likely split into 3 pages:

• How to write an email (& getting it reviewed)
• How to send on Mailchimp
• How to send on Google Groups