docs: how to register existing models

README.md

@@ -74,6 +74,8 @@ urlpatterns = [
 After installation, it is required that admin classes are going to inherit from custom `ModelAdmin` available in `unfold.admin`.
 
 ```python
+# admin.py
+
 from django.contrib import admin
 from unfold.admin import ModelAdmin
 
@@ -83,6 +85,25 @@ class CustomAdminClass(ModelAdmin):
     pass
 ```
 
+**Note:** Registered admin models coming from third party packages are not going to properly work with Unfold because of parent class. By default, these models are registered by using `django.contrib.admin.ModelAdmin` but it is needed to use `unfold.admin.ModelAdmin`. Solution for this problem is to unregister model and then again register it back by using `unfold.admin.ModelAdmin`.
+
+```python
+# admin.opy
+from django.contrib import admin
+from django.contrib.auth.admin import UserAdmin as BaseUserAdmin
+from django.contrib.auth.models import User
+
+from unfold.admin import ModelAdmin
+
+
+admin.site.unregister(User)
+
+
+@admin.register(User)
+class UserAdmin(BaseUserAdmin, ModelAdmin):
+    pass
+```
+
 ## Configuration
 
 ### Available settings.py options