update readme

Author: gracepark

README.md

@@ -55,6 +55,11 @@ export default [
 ]
 ```
 
+> [!NOTE]
+> If you configured the `filenames/match-regex` rule, please note we have adapted the match regex rule into `eslint-plugin-github` as the original `eslint-filenames-plugin` is no longer maintained and needed an ESLint v9 update. Please update the name to `github/filenames-match-regex` and keep the same configuration. For e.g.:
+
+> `'github/filenames-match-regex': ['error', '^[a-z0-9-]+(.[a-z0-9-]+)?$']`
+
 The available configs are:
 
 - `internal`