docs update

docs/configuration/session.md

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+
+### Configuring Session service to use database
+
+First, create a table ```sessions``` with this sql:
+```
+CREATE TABLE `sessions` (
+      `sess_id` varbinary(128) NOT NULL,
+      `sess_data` blob NOT NULL,
+      `sess_lifetime` mediumint(9) NOT NULL,
+      `sess_time` int(10) unsigned NOT NULL,
+      PRIMARY KEY (`sess_id`)
+) CHARSET=utf8 COLLATE=utf8_bin;
+```
+
+Then, open ```configuration.php``` and update Auth handler under section ```services``` to something like this:
+
+```
+        'Filegator\Services\Session\SessionStorageInterface' => [
+            'handler' => '\Filegator\Services\Session\Adapters\SessionStorage',
+            'config' => [
+                'session_handler' => 'database',
+                'available' => [
+                    'database' => function () {
+                        $handler = new \Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler(
+                            'mysql://root:password@localhost:3360/filegator'
+                        );
+
+                        return new \Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage([], $handler);
+                    },
+                ],
+            ],
+        ],
+
+```
+Don't forget to enter correct mysql username, password, and database.
+
+
+### Tweaking session options
+
+The Underying Symfony session [component](https://github.com/symfony/symfony/blob/4.4/src/Symfony/Component/HttpFoundation/Session/Storage/NativeSessionStorage.php) constructor accepts an array options.
+For example you can pass ```cookie_lifetime``` parameter and extend session lifetime like this:
+```
+        'Filegator\Services\Session\SessionStorageInterface' => [
+            'handler' => '\Filegator\Services\Session\Adapters\SessionStorage',
+            'config' => [
+                'session_handler' => 'database',
+                'available' => [
+                    'database' => function () {
+                        $handler = new \Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler(
+                            'mysql://root:password@localhost:3360/filegator'
+                        );
+
+                        return new \Symfony\Component\HttpFoundation\Session\Storage\NativeSessionStorage([
+                            'cookie_lifetime' => 365 * 24 * 60 * 60, // one year
+                        ], $handler);
+                    },
+                ],
+            ],
+        ],
+
+```