Add clarifying comments about bash usage in build scripts

Co-authored-by: johndoe6345789 <224850594+johndoe6345789@users.noreply.github.com>

scripts/create_image.sh

@@ -1,6 +1,8 @@
 #!/bin/bash
 # SparkOS Image Creation Script
 # Creates a bootable dd-able disk image
+# Note: This script runs on the host system and uses bash for ${BASH_SOURCE}
+# The target system uses busybox sh instead.
 
 set -e