Move `master` branch to `main` about crancache

[jennybc]

GitHub's support for default branch renaming means that, in general, pull requests that target the default branch will be correctly re-targetted.

However, there are some edge cases, where this is not true. Some pull requests are automatically closed when the default branch is renamed and they cannot be re-opened. This happens when the PR-making branch, fork, or user no longer exists. (Literally, it appears to boil down to whether HEAD of the PR branch is available for whatever behind-the-scenes magic is happening.)

There is 1 open pull request in this repo that is at risk of auto-closing:

#42

A way to "rescue" the work on such a PR is described in isaacs/github#168 (comment). Here's the TL;DR:

If there is a PR displaying unknown repository after the fork was deleted, and you want to resurrect that PR, simply type:

git fetch origin refs/pull/123/head:foo

substituting (if necessary) origin for the remote pointing at the target repo, 123 for the PR number, and foo for the name of the local branch you want created to point to the head of the PR.

Then you can simply git checkout foo ... and resubmit a new one ....

message id: hardhearted_newt

[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