[TwigBundle] Add documentation about generating absolute URL with the…

… asset function

book/templating.rst

@@ -991,6 +991,22 @@ assets won't be cached when deployed. For example, ``/images/logo.png`` might
 look like ``/images/logo.png?v2``. For more information, see the :ref:`ref-framework-assets-version`
 configuration option.
 
+.. versionadded:: 2.5
+    Absolute URLs for assets were introduced in Symfony 2.5.
+
+If you need absolute URLs for assets, you can set the third argument (or the
+``absolute`` argument) to ``true``:
+
+.. configuration-block::
+
+    .. code-block:: html+jinja
+
+        <img src="{{ asset('images/logo.png', absolute=true) }}" alt="Symfony!" />
+
+    .. code-block:: html+php
+
+        <img src="<?php echo $view['assets']->getUrl('images/logo.png', null, true) ?>" alt="Symfony!" />
+
 .. index::
    single: Templating; Including stylesheets and JavaScripts
    single: Stylesheets; Including stylesheets

components/templating/helpers/assetshelper.rst

@@ -47,6 +47,23 @@ You can also specify a URL to use in the second parameter of the constructor::
 
 Now URLs are rendered like ``http://cdn.example.com/images/logo.png``.
 
+.. versionadded:: 2.5
+    Absolute URLs for assets were introduced in Symfony 2.5.
+
+You can also use the third argument of the helper to force an absolute URL:
+
+.. code-block:: html+php
+
+   <img src="<?php echo $view['assets']->getUrl('images/logo.png', null, true) ?>">
+   <!-- renders as:
+   <img src="http://yourwebsite.com/foo/bar/images/logo.png">
+   -->
+
+.. note::
+
+    If you already set a URL in the constructor, using the third argument of
+    ``getUrl`` will not affect the generated URL.
+
 Versioning
 ----------