buster-updates

In the two Debian Buster installations I did while Buster was still in Testing, the /etc/apt/sources.list file does not contain the buster-updates (previously "volatile") lines. I don't think that suite comes into play until the Stable release.

The Debian Wiki's "SourcesList" page (https://wiki.debian.org/SourcesList) shows example sources.list files for Buster, and they include the buster-updates suite. So I went ahead and added them here.

Here's my edited sources.list file in Buster Xfce, which I installed from Testing way back in April: