updated release script

scripts/set-dmg-icon.swift

@@ -0,0 +1,8 @@
+import AppKit
+// Reuse the approved application icon; no artwork or user files are altered.
+guard CommandLine.arguments.count == 3,
+      let icon = NSImage(contentsOfFile:CommandLine.arguments[1]),
+      NSWorkspace.shared.setIcon(icon,forFile:CommandLine.arguments[2],options:[]) else {
+    fputs("Could not set the disk image Finder icon.\n",stderr)
+    exit(1)
+}