BREAKING CHANGE: This moves helpful.el out of core into :lang
emacs-lisp. Since most (all) people have this module enabled, this
shouldn't make a difference for most people, but if you're one of the
few that don't have :lang emacs-lisp enabled, Doom will revert to using
Emacs' built-in help.el and describe-* commands.
Others can also disable helpful with (package! helpful :disable t) if
they prefer Emacs' built-in help system, which wasn't possible before,
because it was a core package.
This was done as part of an ongoing effort to slim down Doom's core in
preparation for v3.
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