docs: describe how to configure via Flat Config

README.md

@@ -62,6 +62,29 @@ Configure it in `.eslintrc`:
 }
 ```
 
+### Flat Config (ESLint ≥v9 default)
+
+```js
+// eslint.config.js
+
+import { FlatCompat } from "@eslint/eslintrc"
+import path from "path"
+import { fileURLToPath } from "url"
+
+// mimic CommonJS variables -- not needed if using CommonJS
+const __filename = fileURLToPath(import.meta.url)
+const __dirname = path.dirname(__filename)
+
+const compat = new FlatCompat({
+  baseDirectory: __dirname
+})
+
+export default [
+  // mimic ESLintRC-style extends
+  ...compat.extends('plugin:financial/recommended'),
+]
+```
+
 ## Contributing
 
 1. Fork it!