docs: add documentation for labelFn of SimpleFormIterator

Author: iamstiil

docs/Inputs.md

@@ -1211,6 +1211,19 @@ import { ArrayInput, SimpleFormIterator, DateInput, TextInput } from 'react-admi
 </ArrayInput>
 ```
 
+Furthermore, if you want to customize the label displayed for each item, you can pass a function to `SimpleFormIterator` via the `labelFn` prop.
+
+```jsx
+import { ArrayInput, SimpleFormIterator, DateInput, TextInput } from 'react-admin';
+
+<ArrayInput source="backlinks">
+    <SimpleFormIterator labelFn={(index) => `${index + 1}. link`}>
+        <DateInput source="date" />
+        <TextInput source="url" />
+    </SimpleFormIterator>
+</ArrayInput>
+```
+
 **Note**: `SimpleFormIterator` only accepts `Input` components as children. If you want to use some `Fields` instead, you have to use a `<FormDataConsumer>` to get the correct source, as follows:
 
 ```jsx