Update README.md

README.md

@@ -6,6 +6,23 @@ A silverstripe dropdown field that has it's options populated via ajax, based on
 
 SilverStripe 3
 
-##Usage
+##Usage example
 
-TODO!
+```php
+// 1. Create a callable function that returns an array of options for the DependentDropdownField. When the value of the field it depends on changes, this function is called passing the updated value as the first parameter ($val)
+$datesSource = function($val){	
+	if($val == 'one'){
+	  // return appropriate options array if the value is one.
+	}
+	if($val == 'two'){
+	  // return appropriate options array if the value is two.
+	}
+}; 
+
+$fields = FieldList::create(
+  // 2. Add your first field to your field list, 
+	$fieldOne = DropdownField::create('FieldOne','Field One', array('one' => 'One', 'two' => 'Two'),
+	// 3. Add your DependentDropdownField, setting the source as the callable function you created and setting the field it depends on to the appropriate field
+	DependentDropdownField::create('FieldTwo','Field Two', $datesSource)->setDepends($fieldOne)
+);
+```