Install Tailscale on .deb based Linux distributions

Packages are available for the following distributions:

• Ubuntu 16.04 LTS (xenial)
• Ubuntu 18.04 LTS (bionic)
• Ubuntu 19.10 (eoan)
• Ubuntu 20.04 LTS (focal)
• Debian Stretch (oldstable)
• Debian Buster (stable)
• Debian Bullseye (testing)
• Debian Sid (unstable)
• Raspbian (for Raspberry Pi)