X.U.Run: Improve and add documentation
X.U.Run: Improve and add documentation

This adds documentation for the new EDSL, as well as small fixes to
existing docs.

Importantly, I've added myself as a maintainer of the file (even though
we don't really care about this at this point) and updated the
copyright; the changes seem large enough to warrant this.

xmonad/xmonad-contrib,xmonad/xmonad-contrib