explain use [Closes #462]

Author: dg

doc/cs/quickstart/comments.texy

@@ -47,7 +47,7 @@ Nette Framework využívá koncept *komponent*. **Komponenta** je znovupoužitel
 /--php
 	protected function createComponentCommentForm()
 	{
-		$form = new Form;
+		$form = new Form; // means Nette\Application\UI\Form
 
 		$form->addText('name', 'Jméno:')
 			->setRequired();

doc/en/quickstart/comments.texy

@@ -46,7 +46,7 @@ Nette Framework has a concept of *components*. A **component** is a reusable cla
 /--php
 	protected function createComponentCommentForm()
 	{
-		$form = new Form;
+		$form = new Form; // means Nette\Application\UI\Form
 
 		$form->addText('name', 'Your name:')
 			->setRequired();