Add a .desktop file

[Susurrus]

A .desktop file is necessary so that applications are visible through the Gnome Shell launcher. It'd be useful if this was already in the repo and people didn't have to make their own for the application to be found. I had been playing with Radeon Profile and it has an example one for reference: https://github.com/marazmista/radeon-profile/blob/master/radeon-profile/extra/radeon-profile.desktop