Document changes and release 5.12.2pureos3 of linux-librem5

Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
2 jobs for pureos/5.12.2pureos3 in 82 minutes and 31 seconds (queued for 28 minutes and 16 seconds)
latest
Status Job ID Name Coverage
  Build
passed #352688
librem5
build:aarch64

00:58:36

passed #352689
librem5:arm64
build:deb

01:10:42