docs: Process docs for VC Newsletter

[tkshill]

Description

VC has been actively maintaining a monthly newsletter for several years. Traditionally this has been handled by the Community Maintainers. We should add process docs for the procedure of creating and maintaining the content for the newsletter.

Goals

• More accountability for creating, maintaining and organizing the newsletter
• Easier access to volunteer support for newsletter creation
• Easier to edit ongoing newsletter prep
• Easier to coordinate with other communication channels (like the website)
• Easier for future migration to other platforms, or automation

Items needed for completion

• Issue template for newsletter (to be created and closed monthly, similar to the virtualcoffee.io monthly challenge updates)
• Platform-agnostic description of procedure
• A guide on where and how to source all newsletter content section (goals and wins, gratitude, recaps, new events, etc.)