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 12 seconds
Status Job ID Name Coverage
  Package
passed #363602
librem5
package-pureos-byzantium

00:00:38

passed #363603
librem5:arm64
package-pureos-byzantium:arm64

00:02:12

 
  Test Package
passed #363604
librem5
autopkgtest-pureos-byzantium-package

00:00:46

passed #363605
librem5
lintian-pureos-byzantium-package

00:00:41