Update the ReadMe and Getting Started Guide

[McEileen]

I will update the ReadMe and Getting Started Guide to make it more current. Main areas to update:

• Code of conduct team
• Technical maintainers
• Add links to getting started guide for section headings
• Either remove non-mac install guidelines or make them (possibly ask a non-mac user for input?)
• Remove links to Chi Hack night working group and slack
• Add link to current slack
• Current meeting schedule
• Tech stack changes, namely, using Rspec instead of Minitest