Document changes and release 5.12.2pureos4~amber1 of linux-librem5

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
2 jobs for pureos/amber-phone in 63 minutes and 28 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #353790
librem5
build:aarch64

00:19:39

passed #353791
librem5:arm64
build:deb

01:03:27