Update instructions to setup automatic updates for Ubuntu and Debian
Currently, the page [https://trac.torproject.org/projects/tor/wiki/TorRelayGuide/DebianUbuntuUpdates] only refers to Debian, and uses the syntax used in the Debian Wiki. Ubuntu, on the other hand, uses a different syntax.
It's possible that both ways work on both distributions, or that Debian is using an older syntax that doesn't work on Ubuntu (I can't test that now).
I propose linking to both wiki pages (Ubuntu and Debian) for the Unattended Upgrades configuration, while informing the reader that they must set the TorProject origin as well. The rest of the instructions are not directly related to Tor, and will only confuse the reader if eventually it is no longer up-to-date with the instructions given on their official documentation.
Debian Wiki [https://wiki.debian.org/UnattendedUpgrades]