Added a cookbook entry about building single command applications

This documents the way to achieve the use case requested in
symfony/symfony#3857

Author: stof

cookbook/console/index.rst

@@ -7,3 +7,4 @@ Console
     console_command
     usage
     generating_urls
+    single_command_tool

cookbook/console/single_command_tool.rst

@@ -0,0 +1,48 @@
+.. index::
+   single: Console; Single command application
+
+How to build an Application with a single Command
+=================================================
+
+When building a command line tool, you may not need to provide several commands.
+In such case, having to pass the command name each time is tedious. Fortunately,
+it is possible to remove this need by extending the application::
+
+    namespace Acme\Tool;
+
+    use Symfony\Component\Console\Application;
+    use Symfony\Component\Console\Input\InputInterface;
+
+    class MyApplication extends Application
+    {
+        /**
+         * Gets the name of the command based on input.
+         *
+         * @param InputInterface $input The input interface
+         *
+         * @return string The command name
+         */
+        protected function getCommandName(InputInterface $input)
+        {
+            return 'my_command';
+        }
+
+        /**
+         * Gets the default commands that should always be available.
+         *
+         * @return array An array of default Command instances
+         */
+        protected function getDefaultCommands()
+        {
+            // Keep the core default commands to have the HelpCommand
+            // which is used when using the --help option
+            $defaultCommands = parent::getDefaultCommands()
+
+            $defaultCommands[] = new MyCommand();
+
+            return $defaultCommands;
+        }
+    }
+
+When calling your console script, the command `MyCommand` will then always
+be used, without having to pass its name.

cookbook/map.rst.inc

@@ -29,6 +29,7 @@
   * :doc:`/cookbook/console/console_command`
   * :doc:`/cookbook/console/usage`
   * :doc:`/cookbook/console/generating_urls`
+  * :doc:`/cookbook/console/single_command_tool`
 
 * :doc:`/cookbook/controller/index`