Update .gitignore example

As confirmed by WouterJ on Stack Overflow [1], the example
.gitignore file [2] is not up-to-date.

This commit updates the documentation to reflect the current state
of the .gitignore file that is included in the Symfony Standard
Edition distribution [3].

[1] http://stackoverflow.com/q/23437768/1001110
[2] http://symfony.com/doc/current/cookbook/workflow/new_project_git.html#initial-project-setup
[3] https://github.com/symfony/symfony-standard/blob/master/.gitignore

Author: nicwortel

cookbook/workflow/new_project_git.rst

@@ -32,11 +32,16 @@ git repository:
    .. code-block:: text
 
         /web/bundles/
-        /app/bootstrap*
+        /app/bootstrap.php.cache
         /app/cache/*
+        /app/config/parameters.yml
         /app/logs/*
+        !app/cache/.gitkeep
+        !app/logs/.gitkeep
+        /build/
         /vendor/
-        /app/config/parameters.yml
+        /bin/
+        /composer.phar
 
 .. tip::