Add dependency

[wick3dr0se]

RME won't compile on Arch Linux without GLUT. It threw error missing GLUT and failed cmake..
The dependency below should be added to the compile guide for Arch users as well as wxgtk3-dev as an optional package which is currently necessary to build RME 3.6.1+ and can be installed from the AUR

sudo pacman -S freeglut