improve doc storing

Form/PersonDocumentType.php

@@ -74,6 +74,7 @@ class PersonDocumentType extends AbstractType
             ])
             ->add('date', ChillDateType::class)
             ->add('category', EntityType::class, array(
+                'placeholder' => 'Choose a document category',
                 'class' => 'ChillDocStoreBundle:DocumentCategory',
                 'query_builder' => function (EntityRepository $er) {
                     return $er->createQueryBuilder('c')