Move `master` branch to `main`

[jennybc]

The master branch of this repository will soon be renamed to main, as part of a coordinated change across several GitHub organizations (including, but not limited to: tidyverse, r-lib, tidymodels, and sol-eng). We anticipate this will happen by the end of September 2021.

That will be preceded by a release of the usethis package, which will gain some functionality around detecting and adapting to a renamed default branch. There will also be a blog post at the time of this master --> main change.

The purpose of this issue is to:

• Help us firm up the list of targetted repositories
• Make sure all maintainers are aware of what's coming
• Give us an issue to close when the job is done
• Give us a place to put advice for collaborators re: how to adapt

message id: euphoric_snowdog

[jennybc]

This repo was selected for an early switch from master to main, to help refine our process for the larger effort. Thank you for your service!

When we scale this up to all ~350 repos, there will be a public announcement pointing to a blog post about this change, pointing out the usethis functions available to package maintainers and contributors to support default branch renaming.

In the meantime, this blog post is available in draft form and can be read here.

message id: exalted_aphid