rename master branch to main

[longlho]

master as a history of being used in the context of slavery. GitHub also sets the default branch as main when you create a new repo already. We should rename the main branch.

Thoughts?

[buschtoens]

Much in favor! I long wanted to do this, but kept putting it off as to not accidentally break things.

[longlho]

hmm I pushed main but cannot switch default branch. @jasonmit can u give me perm?

[jasonmit]

@longlho made you an admin, feel free to make the update!