doc : update comment on submitForm in the LiveComponent testing doc

Author: yalit

src/LiveComponent/doc/index.rst

@@ -3733,6 +3733,8 @@ uses Symfony's test client to render and make requests to your components::
             ;
 
             // Submit form data
+	    // 'form' is the name of the form you're submitting (here FormType). 
+            // e.a : form submitted is EntityCreationType the name of your form would be 'entity_creation' and should replace 'form' in the below submitForm call
             $testComponent
                 ->submitForm(['form' => ['input' => 'value']], 'save');