[Cookbook] [Deployment] Added note about Nginx

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.3+
| Fixed tickets |

cookbook/deployment/heroku.rst

@@ -106,6 +106,15 @@ directory of the application and add just the following content:
 
     web: bin/heroku-php-apache2 web/
 
+.. note::
+
+    Nginx is also available on Heroku. If you prefer to use it, you can create a
+    Nginx config file (``nginx_app.conf`` for instance) to point from Procfile as described in `Heroku docs`_:
+
+    .. code-block:: text
+
+        web: bin/heroku-php-nginx -C nginx_app.conf web/
+
 If you prefer working on the command console, execute the following commands to
 create the ``Procfile`` file and to add it to the repository:
 
@@ -244,3 +253,4 @@ You should be seeing your Symfony application in your browser.
 .. _`verified that the RSA key fingerprint is correct`: https://devcenter.heroku.com/articles/git-repository-ssh-fingerprints
 .. _`post-install-commands`: https://getcomposer.org/doc/articles/scripts.md
 .. _`config vars`: https://devcenter.heroku.com/articles/config-vars
+.. _`Heroku docs`: https://devcenter.heroku.com/articles/custom-php-settings#nginx