Integrate meta-guf-distro/adapt_README

Commit: https://git.seco.com/seco-ne/yocto/layers/meta-guf-distro/-/commit/81bd01a9f04b974ca44acbef6487d62118dd9d5d

README: Adapt the README for SECO

Rename the distribution to SECO Northern Europe distribution and reference the manifest as the main source of information.

BCS 746-000659