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

README.md

 # meta-guf-distro
-See Readme in meta-guf-machine for project information.
+See README.md in the manifest project for project information.
 
-This layer contains everything to build the guf distribution, mainly 
+This layer contains everything to build the standard SECO Northern Europe distribution,  containing all tools and packages generally used on SECO Northern Europe (by Garz & Fricke) devices.
 
-bitbake guf-image
+The main image is the ```guf-image``` built using:
+
+```bitbake guf-image```
 
-containing all tools and packages generally used on  G&F devices.
 In a perfect world there should be no dependencies to the meta-guf-machine
-layer and the guf-image should be buildable for other machines too.
+layer and the guf-image should be buildable for other machines too. This, however, is not tested, verified or supported.