Add build-iso.sh script for local image generation

build-iso.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+# Write out the current channels to be included with the image
+guix describe -f channels > channels.scm
+
+# Build the image and copy it to the current directory
+image=$(guix system image -t iso9660 installer.scm)
+echo "Built image: $image"
+cp $image ./guix-installer.iso