Update documentation

Author: CWAscend

docs/validation/introduction.md

@@ -132,6 +132,28 @@ class SongData extends Data
 }
 ```
 
+The above example will override the automatically inferred rules. If you want the manual rules to be merged with the automatically inferred rules, you can use the `MergeRules` attribute:
+
+```php
+#[MergeRules]
+class SongData extends Data
+{
+    public function __construct(
+        public string $title,
+        public string $artist,
+    ) {
+    }
+    
+    public static function rules(): array
+    {
+        return [
+            'title' => ['max:255'],
+            'artist' => ['max:255'],
+        ];
+    }
+}
+```
+
 You can read more about manual rules in its [dedicated chapter](/docs/laravel-data/v4/validation/manual-rules).
 
 ### Using the container