Update README.md

README.md

@@ -6,7 +6,15 @@ graph TD;
     C-->D;
     
 ```    
-    
+
+```mermaid
+erDiagram;
+    t_client_user  ||--o{ t_client_user_device : has;
+    t_client_user_device }|--|| t_user_device_group : related;
+
+```
+
+
 ```mermaid
 erDiagram
     t_client_user  ||--o{ t_client_user_device : has