-f is necessary when there are changes to your system that Doom needs to
pick up when running 'doom refresh'. It won't do anything if your doom
dotfiles haven't visibly changed, which won't be the case if you are
installing, say, mu4e or vterm, through your system package manager.
What was initially a time-saving mechanic has become a trap for
beginners, so I've made -f its default behavior and its previous
behavior opt-in with the -n / --if-necessary switches.
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