feature #7570 Add MicroKernelTrait advanced example run section (dominikhajduk)

This PR was merged into the 2.8 branch.

Discussion
----------

Add MicroKernelTrait advanced example run section

PR after [issue #7348](#7348) reported by @olberger.
Improved [MicroKernel advanced example](http://symfony.com/doc/current/configuration/micro_kernel_trait.html#advanced-example-twig-annotations-and-the-web-debug-toolbar). Mentioned that build-in web server need to be run in `web/` directory.

Commits
-------

6e9bb73 Add MicroKernelTrait advanced example run section

Author: wouterj

configuration/micro_kernel_trait.rst

@@ -88,7 +88,7 @@ That's it! To test it, you can start the built-in web server:
 
 Then see the JSON response in your browser:
 
-> http://localhost:8000/random/10
+    http://localhost:8000/random/10
 
 The Methods of a "Micro" Kernel
 -------------------------------
@@ -319,6 +319,17 @@ this:
     ├─ composer.json
     └─ composer.lock
 
+As before you can use PHP built-in server:
+
+.. code-block:: bash
+
+    cd web/
+    $ php -S localhost:8000
+
+Then see webpage in browser:
+
+    http://localhost:8000/random/10
+
 Hey, that looks a lot like a *traditional* Symfony application! You're right: the
 ``MicroKernelTrait`` *is* still Symfony: but you can control your structure and
 features quite easily.