usage example for nested form document

Author: mutec

README.md

@@ -1,2 +1,32 @@
 # de.mysterycode.wcf.formBuilder.extension
 
+# Nested form fields
+Sometimes you want to store some data serialzed as an array but you want to have a form field for every property.
+
+The form builder introduced in WSC 5.2 is currently not able to handle this case properly, so there is some sort of workaround required. 
+
+Usage example:
+```PHP
+use wcf\system\form\builder\container\DummyFormContainer;
+use wcf\system\form\builder\container\FormContainer;
+use wcf\system\form\builder\data\processor\PrefixedFormDataProcessor;
+use wcf\system\form\builder\NestedFormDocument;
+use wcf\system\form\builder\field\TextFormField;
+
+$this->form = NestedFormDocument::create('DummyAdd');
+$this->form->appendChildren([
+	DummyFormContainer::create('additionalData')
+        ->appendChildren([
+            FormContainer::create('foo')
+                ->label('wcf.dummy.foo')
+                ->appendChildren([
+                    TextFormField::create('additionalData[foo][bar]')
+                        ->label('wcf.dummy.foo.bar')
+                ])
+        ])
+    ]);
+$this->form->getDataHandler()->addProcessor(new PrefixedFormDataProcessor('additionalData', 'additionalData'));
+```
+
+###Attention:
+You have to serialize the array manually before writing it to your database!