Add undo-fu for evil mode

[jacksonludwig]

I may be wrong, but according to evil mode's instructions, an undo package should be installed to correctly simulate vim's undo (undo-fu, undo-tree, or emacs 28's undo-redo). Just a (use-package undo-fu) and (setq evil-undo-system 'undo-fu) should be enough I think.

[daviwil]

Yep, I need to add a note for that in the evil-mode video, thanks for bringing it up!