Update Form example

Without specifying the action, Turbo redirect the full page to /.

name="product_new" is not necessary in this specific example, it however may help newcomer to understand they can have separate route for this action (even if not recommended by the Symfony Form docs).

Not sure if it is a bug in turbo or me doing wrong, adding this fixes it.

Author: pierrejoye

src/Turbo/README.md

@@ -97,12 +97,16 @@ automatically:
 
 ```php
 /**
- * @Route("/product/new")
+ * @Route("/product/new", name="product_new")
  */
 public function newProduct(Request $request): Response
 {
     return $this->handleForm(
-        $this->createForm(ProductFormType::class),
+        $this->createForm(ProductFormType::class, null,
+        [
+            'action' => $this->generateUrl('product_new'),
+        ]
+        ),
         $request,
         function (FormInterface $form) {
             // save...
@@ -176,6 +180,17 @@ $builder
         ]
     ]);
 ```
+> **NOTE Turbo ^7.0.0-beta.5:**
+> If Turbo ^7.0.0-beta.5 or lower (may be still valid with future version), there is a bug with turbo-frame and form submit. F.e., a link to add a product will work the 1st time, the frame will have the new product form, on submit, the frame will be updated using the products listing. At this point the new link won't work anymore. This is cache issue in Turbo. To avoid it add a ramdom value as get parameter, microtime(true) will make it unique for one client:
+
+```php
+return $this->redirectToRoute('school', ['rmd' => time()], Response::HTTP_SEE_OTHER);
+```
+and in the listing template:
+
+```php
+<a data-turbo-action="replace" href="/school/new?rdm={{ rdm }}">Add Product</a>
+```
 
 #### More Turbo Drive Info