minor #102 [WIP] moving SwiftmailerBundle docs to bundle repo (snoek09)

This PR was squashed before being merged into the 2.3-dev branch (closes #102).

Discussion
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[WIP] moving SwiftmailerBundle docs to bundle repo

Added installation chapter.

Easy picks on bundle side from symfony/symfony-docs#4983

Commits
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ff2ffda [WIP] moving SwiftmailerBundle docs to bundle repo

Author: fabpot

Resources/doc/index.rst

@@ -0,0 +1,45 @@
+Installation
+============
+
+Step 1: Download the Bundle
+---------------------------
+
+Open a command console, enter your project directory and execute the
+following command to download the latest stable version of this bundle:
+
+.. code-block:: bash
+
+    $ composer require symfony/swiftmailer-bundle "~2.3"
+
+This command requires you to have Composer installed globally, as explained
+in the `installation chapter`_ of the Composer documentation.
+
+Step 2: Enable the Bundle
+-------------------------
+
+Then, enable the bundle by adding the following line in the ``app/AppKernel.php``
+file of your project:
+
+.. code-block:: php
+
+    <?php
+    // app/AppKernel.php
+
+    // ...
+    class AppKernel extends Kernel
+    {
+        public function registerBundles()
+        {
+            $bundles = array(
+                // ...
+
+                new Symfony\Bundle\SwiftmailerBundle\SwiftmailerBundle(),
+            );
+
+            // ...
+        }
+
+        // ...
+    }
+
+.. _`installation chapter`: https://getcomposer.org/doc/00-intro.md