Please rename the primary/default branch to something more inclusive

[gwhitney]

I am filing this issue to request that this project abandon the old, typical name for the primary/default branch of the repository in favor of a more neutral name like "main" or "develop." This request is part of a general industry shift to using more inclusive language. I would file a pull request, but I am not sure that such a renaming can be done via pull request. Thanks very much for your consideration.