add comment describing file and error log explaining the format

format.js

@@ -1,3 +1,15 @@
+/**
+ * This file is used for checking and updating the format of the JSON file.
+ *
+ * You can check the format via `node format.js --check` and regenerate the
+ * file with the correct formatting using `node format.js --generate`.
+ *
+ * The formatting logic uses `JSON.stringify` with 2 spaces, which will keep
+ * separating commas on the same line as any closing character. This technique
+ * was chosen for simplicty and to align with common default JSON formatters,
+ * such as VSCode.
+ */
+
 const fs = require("fs");
 const path = require("path");
 
@@ -15,6 +27,7 @@ if (process.argv[2] === "--generate") {
 if (process.argv[2] === "--check") {
     if (updated !== original) {
         console.error("JSON file format is wrong. Run `node format.js --generate` to update.");
+        console.error("Format must be 2 spaces, with newlines for objects and arrays, and separating commas on the line with the previous closing character.");
         process.exit(1);
     }
 }