Sane PATH on graphical macOS

[PythonNut]

Current plan: leverage exec-path-from-shell using the trick from doom-emacs.

Useful for: #105, #101

[raxod502]

See e.g. https://github.com/raxod502/radian/blob/f8967de3a5a1f84b3546bd57dd6226a85bd69a55/emacs/radian.el#L429-L474