Update changelog

Let's have this in 0.0.20 so the `Breaks:` in librem5-base-defaults
stays correct.
4 jobs for pureos/0.0.20pureos1 in 2 minutes and 12 seconds
latest
Status Job ID Name Coverage
  Package
passed #363629
librem5
package-pureos-byzantium

00:00:38

passed #363630
librem5:arm64
package-pureos-byzantium:arm64

00:02:11

 
  Test Package
passed #363631
librem5
autopkgtest-pureos-byzantium-package

00:00:47

passed #363632
librem5
lintian-pureos-byzantium-package

00:00:41