This contains a bunch of fixes:

• fixes #19 (closed) by adding a necessary sudo
• fixes #17 (closed) by adding a link to backports instructions
• fixes #18 (closed) by adding a hint for Ubuntu versions <18.04; Debian stable (buster) now features Gnome 3.30 (this renders !8 (closed) obsolete)
• renames Archlinux to Arch Linux