website/docs: added example for custom user attributes (#2406)

* added example for custom user attributes

* simplified example

Co-authored-by: croudsarabi <constantin.roudsarabi@andrena.de>

website/docs/expressions/_user.md

@@ -0,0 +1,9 @@
+- `user`: The current user. This may be `None` if there is no contextual user. See ([User](../user-group/user.md#object-attributes))
+
+Example:
+
+```python
+return {
+  "custom_attribute": request.user.attributes.get("custom_attribute", "default"),
+}
+```

website/docs/property-mappings/expression.mdx

@@ -17,6 +17,9 @@ import Objects from '../expressions/_objects.md'
 
 <Objects />
 
-- `user`: The current user. This may be `None` if there is no contextual user. See ([User](../user-group/user.md#object-attributes))
+import User from '../expressions/_user.md'
+
+<User />
+
 - `request`: The current request. This may be `None` if there is no contextual request. See ([Django documentation](https://docs.djangoproject.com/en/3.0/ref/request-response/#httprequest-objects))
 - Other arbitrary arguments given by the provider, this is documented on the Provider/Source.