doc: minor updates to guix README

contrib/guix/INSTALL.md

@@ -72,11 +72,11 @@ writing (July 2021). Guix is expected to be more widely packaged over time. For
 an up-to-date view on Guix's package status/version across distros, please see:
 https://repology.org/project/guix/versions
 
-### Debian 11 (Bullseye)/Ubuntu 21.04 (Hirsute Hippo)
+### Debian / Ubuntu
 
 Guix v1.2.0 is available as a distribution package starting in [Debian
 11](https://packages.debian.org/bullseye/guix) and [Ubuntu
-21.04](https://packages.ubuntu.com/hirsute/guix).
+21.04](https://packages.ubuntu.com/search?keywords=guix).
 
 Note that if you intend on using Guix without using any substitutes (more
 details [here][security-model]), v1.2.0 has a known problem when building GnuTLS