Fixed syntax issues and provided more information

Author: javiereguiluz

book/forms.rst

@@ -1060,12 +1060,13 @@ that will house the logic for building the task form::
 .. caution::
 
     The ``getName()`` method returns the identifier of this form "type". These
-    identifiers must be unique in the application and, unless you want to override
-    a built-in type, they should be different from the default Symfony types.
+    identifiers must be unique in the application. Unless you want to override
+    a built-in type, they should be different from the default Symfony types
+    and from any type defined by a third-party bundle installed in you application.
     Consider prefixing your types with ``app_`` to avoid identifier collisions.
 
 This new class contains all the directions needed to create the task form. It can
-be used to quickly build a form object in the controller:
+be used to quickly build a form object in the controller::
 
     // src/AppBundle/Controller/DefaultController.php