docs(#41): update README

Author: dukeluo

README.md

@@ -28,6 +28,54 @@ npm install eslint-plugin-check-file --save-dev
 
 ## Usage
 
+### Flat Config
+
+```javascript
+import checkFile from 'eslint-plugin-check-file';
+
+export default [
+  {
+    files: ['src/**/*'],
+    plugins: {
+      'check-file': checkFile,
+    },
+    rules: {
+      'check-file/no-index': 'error',
+      'check-file/filename-blocklist': [
+        'error',
+        {
+          '**/*.model.ts': '*.models.ts',
+          '**/*.util.ts': '*.utils.ts',
+        },
+      ],
+      'check-file/folder-match-with-fex': [
+        'error',
+        {
+          '*.test.{js,jsx,ts,tsx}': '**/__tests__/',
+          '*.styled.{jsx,tsx}': '**/pages/',
+        },
+      ],
+      'check-file/filename-naming-convention': [
+        'error',
+        {
+          '**/*.{jsx,tsx}': 'CAMEL_CASE',
+          '**/*.{js,ts}': 'KEBAB_CASE',
+        },
+      ],
+      'check-file/folder-naming-convention': [
+        'error',
+        {
+          'src/**/': 'CAMEL_CASE',
+          'mocks/*/': 'KEBAB_CASE',
+        },
+      ],
+    },
+  },
+];
+```
+
+### `eslintrc`
+
 Add `check-file` to the plugins section of your `.eslintrc` configuration file. You can omit the `eslint-plugin-` prefix:
 
 ```json