minor #9893 Better explain render() and render_esi() functions (javiereguiluz)

This PR was squashed before being merged into the 2.8 branch (closes #9893).

Discussion
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Better explain render() and render_esi() functions

Commits
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fd79440 Better explain render() and render_esi() functions

Author: javiereguiluz

reference/twig_reference.rst

@@ -53,14 +53,21 @@ render
 ``options`` *(optional)*
     **type**: ``array`` **default**: ``[]``
 
-Renders the fragment for the given controller (using the `controller`_ function)
-or URI. For more information, see :doc:`/templating/embedding_controllers`.
+Makes a request to the given internal URI or controller and returns the result.
+It's commonly used to :doc:`embed controllers in templates </templating/embedding_controllers>`.
 
-The render strategy can be specified in the ``strategy`` key of the options.
+.. code-block:: twig
 
-.. tip::
+    {# if the controller is associated with a route, use the path() or
+       url() functions to generate the URI used by render() #}
+    {{ render(path('latest_articles', {num: 5})) }}
+    {{ render(url('latest_articles', {num: 5})) }}
+
+    {# if you don't want to expose the controller with a public URL, use
+       the controller() function to define the controller to be executed #}
+    {{ render(controller('AppBundle:Default:latestArticles', {num: 5})) }}
 
-    The URI can be generated by other functions, like `path`_ and `url`_.
+The render strategy can be specified in the ``strategy`` key of the options.
 
 .. _reference-twig-function-render-esi:
 
@@ -76,13 +83,9 @@ render_esi
 ``options`` *(optional)*
     **type**: ``array`` **default**: ``[]``
 
-Generates an ESI tag when possible or falls back to the behavior of
-`render`_ function instead. For more information, see
-:doc:`/templating/embedding_controllers`.
-
-.. tip::
-
-    The URI can be generated by other functions, like `path`_ and `url`_.
+It's similar to the `render`_ function and defines the same arguments. However,
+it generates an ESI tag when :doc:`ESI support </http_cache/esi>` is enabled or
+falls back to the behavior of `render`_ otherwise.
 
 .. tip::