Add comment explaining use of merge

scripts/merge.js

@@ -1,3 +1,6 @@
+// This is used to merge JSON files (package.json and product.json) and delete a
+// few entries we don't want. It's extremely simple, expects very specific
+// input, and doesn't have any error handling.
 const fs = require("fs");
 
 const a = process.argv[2];