Improve Ubuntu installation instructions
2/6. Install Tails Installer ▸ If you are running Ubuntu ▸ 2. Open a Root Terminal.
No Root Terminal is installed, at least not on a fresh install of Ubuntu GNOME 17.04. Or if it is installed, I think we need to explain better how to open it.
Maybe instead we should explain how to add the tails-installer PPA through the graphical Software & Updates application?