Some Basic App readme updates [skip ci]

README.md

@@ -12,11 +12,14 @@ features to your application.
 DIRECTORY STRUCTURE
 -------------------
 
+      assets/             contains assets definition
       commands/           contains console commands (controllers)
       config/             contains application configurations
       controllers/        contains Web controller classes
+      mails/              contains view files for e-mails
       models/             contains model classes
       runtime/            contains files generated during runtime
+      tests/              contains various tests for the basic application
       vendor/             contains dependent 3rd-party packages
       views/              contains view files for the Web application
       web/                contains the entry script and Web resources
@@ -62,3 +65,24 @@ directly under the Web root.
 http://localhost/basic/web/
 ~~~
 
+
+CONFIGURATION
+-------------
+
+### Database
+
+Edit the file `config/db.php` with real data, for example:
+
+```php
+return [
+	'class' => 'yii\db\Connection',
+	'dsn' => 'mysql:host=localhost;dbname=yii2basic',
+	'username' => 'root',
+	'password' => '1234',
+	'charset' => 'utf8',
+];
+```
+
+**NOTE:** Yii won't create the database for you, this has to be done manually before you can access it.
+
+Also check and edit the other files in the `config/` directory to customize your application.