> init: provide useful advice about init.defaultBranch

> To give ample warning for users wishing to override Git's the fall-back for an unconfigured `init.defaultBranch` (in case we decide to change it in a future Git version), let's introduce some advice that is shown upon `git init` when that value is not set.

https://github.com/git/git/commit/675704c74dd4476f455bfa91e7...

    git tag --contains 675704c74dd4476f455bfa91e72eb9e163317c10 | grep -v rc
    v2.30.0
    v2.30.1
    v2.30.2
    v2.31.0