Document changes and release 5.7.7+librem5.1 of linux-librem5

Signed-off-by: Martin Kepplinger <martink@posteo.de>
2 jobs for imx8-current-librem5 in 49 minutes and 3 seconds (queued for 2 seconds)
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librem5
build:aarch64

00:13:36

passed #280038
librem5:arm64
build:deb

00:49:02