Update admin UI secret example to match (#8618)

k8s/charts/seaweedfs/README.md

@@ -165,8 +165,9 @@ admin:
   enabled: true
   port: 23646
   grpcPort: 33646  # For worker connections
-  adminUser: "admin"
-  adminPassword: "your-secure-password"  # Leave empty to disable auth
+  secret:
+    adminUser: "admin"
+    adminPassword: "your-secure-password"  # Leave empty to disable auth
   
   # Optional: persist admin data
   data:
@@ -191,6 +192,8 @@ If `adminPassword` is set, the admin interface requires authentication:
 
 If `adminPassword` is empty or not set, the admin interface runs without authentication (not recommended for production).
 
+As an alternative, a kubernetes Secret can be used (`admin.secret.existingSecret`).
+
 ### Admin Data Persistence
 
 The admin component can store configuration and maintenance data. You can configure storage in several ways: