Mention monolog service name in the monolog cookbook

[weaverryan]

In the cookbook article where we introduce monolog, we don't ever say how to get it out of the container. We should show a quick example of logging from within a controller, which will show that the service is called logger.

[wouterj]

I think we already have this in the first example of cookbook/logging/monolog:

$logger = $this->get('logger');
$logger->info('I just got the logger');
$logger->err('An error occurred');

It is not very clear that this is from inside a controller, we can do something like this:

# src/Acme/DemoBundle/Controller/LogController.php
namespace Acme\DemoBundle\Controller;

// ...
class LogController extends Controller
{
    public function logAction()
    {
        $logger = $this->get('logger');
        $logger->info('I just got the logger');
        $logger->err('An error occurred');
    }
}

[weaverryan]

Ah, thanks @wouterj! I don't know how I missed that :). I just moved some things around in #2154

Thanks!