Update base branch, naming, documentation, and configuration

[Jkrzy]

Our default git branch for development should be named main.

We'll know we're done when

• The default git branch is main
• Documentation has been updated to reflect the new default branch
• CircleCI configuration has been updated

[cryptofilegsa]

from Hanselman.com blog post, consider: "git branch -m master main" that -m is --move so history isn't changed and "git push -u origin main" to set the upstream at the same time. Looks like this will require all of us changing default branch in our GitHub settings.

[Jkrzy]

Default branch is now main