Signing instructions

src/freedombone-image

     echo ''
     echo "  xz --no-warn --verbose --keep --threads=0 -3 ${IMAGE_FILENAME}"
     echo ''
+    echo $'To sign:'
+    echo ''
+    echo "  gpg -ba ${IMAGE_FILENAME}.xz"
+    echo "  mv ${IMAGE_FILENAME}.xz.asc ${IMAGE_FILENAME}.xz.sig"
+    echo ''
     echo 'To copy to microSD, USB drive or SSD'
     echo ''
     echo '  sudo dd if=/dev/zero of=/dev/sdX bs=32M count=8'