Explain limit-unstable file creation

[dolmen]

In the first block I see this line:

printf 'Package: *\nPin: release a=unstable\nPin-Priority: 150\n' | sudo tee --append /etc/apt/preferences.d/limit-unstable

The tutoratial should explain what it does and why it is necessary.

[dolmen]

Apparently this line comes from the Wireguard official site: https://www.wireguard.com/install/#debian-module-tools

[dolmen]

https://wiki.debian.org/AptConfiguration describes pinning and priority:

When multiple Apt repositories are enabled, a package can exist in several of them. To know which one should be installed, Apt assigns priorities to packages. The default is 500.

• If the packages have the same priority, the package with a higher version number (most recent) wins.
• If packages have different priorities, the one with the higher priority wins.