Update v2_1_1.md (#34)

Author: adamspd

docs/release_notes/v2_1_1.md

@@ -13,7 +13,7 @@ control and customization.
 
 ⚠️ **Important Note**: This version introduces significant database schema changes. Before updating, ensure you follow
 the migration steps outlined in
-the [migration guide](https://github.com/adamspd/django-appointment/tree/main/migration_guide_v2.1.0.md).
+the [migration guide](https://github.com/adamspd/django-appointment/tree/main/docs/migration_guides/v2_1_0.md).
 
 ## New Features ✨