Branch protection guidance wording

[regularfry]

Over here, we say:

- Disable ability to push to the default branch for everyone, admins included (`applies-to-admin` option).

I'm not sure about the default branch wording. What is it that we're specifically trying to do? And can we add some explainer text as to why we think this is a good idea? For some people main will be a development branch with releases cut from another branch, and for others main will be the release branch. main can be viewed as the "default" branch in both cases, but it has different implications either way.