Update changelog

Let's have this in 0.0.20 so the `Breaks:` in librem5-base-defaults
stays correct.
4 jobs for rel in 2 minutes and 11 seconds
Status Job ID Name Coverage
  Package
passed #363621
librem5
package-pureos-byzantium

00:00:43

passed #363622
librem5:arm64
package-pureos-byzantium:arm64

00:02:11

 
  Test Package
passed #363623
librem5
autopkgtest-pureos-byzantium-package

00:00:56

passed #363624
librem5
lintian-pureos-byzantium-package

00:00:48