Update overriding_forms.md

You will need to create a function for interacting with the `name` field, that you have created. The most common one would be something simple like this:

``` php
public function getName()
    return $this->name;
 }
````

After creating the services.xml (or .yml) file, you need to tell Symfony that your new Bundle will load it. So that's why you create a `AcmeUserExtension.php` file under the `DependcyInjection` folder.