Document secure account setup

[ghost]

Issue: Managing multiple email accounts reduces likelihood of timely reply to messages sent to @freeukgenealogy.org.uk address; 2FA introduces complications for account setup; some participants may not feel comfortable completing advanced account configuration w/o an illustrated guide

Proposed resolution: Create Google Doc/PDF with detailed instructions to complete account setup using two factor authentication for security and send/receive emails through primary Gmail account or email client.

Additional considerations: Document -alt GitHub configuration (SSH key and GPG key or fork repo + add primary GitHub account as contributor) for devs who'd prefer not to allow apps like Waffle.io read/write access to all their repos hosted at GitHub.