[Docs] Override Xresources includes a typo in the example

[ahallermed]

What is wrong?

In the documentation, there is a small typo use alt instead of super.

Use a point "." instead of a dash "-" in i3-wm.*

wrong

$ echo "i3-wm-mod: Mod1" >> ~/.config/regolith/Xresources
$ echo "i3-wm-alt: Mod4" >> ~/.config/regolith/Xresources

correct

$ echo "i3-wm.mod: Mod1" >> ~/.config/regolith/Xresources
$ echo "i3-wm.alt: Mod4" >> ~/.config/regolith/Xresources