Adds .Rproj.user, .Rhistory, .Rdata, .httr-oauth, .DS_Store, and
.quarto to your global (a.k.a. user-level) .gitignore. This is good
practice as it decreases the chance that you will accidentally leak
credentials to GitHub. git_vaccinate() also tries to detect and fix the
situation where you have a global gitignore file, but it's missing from your
global Git config.