[config] Update readme

Author: sunkan

README.md

@@ -26,14 +26,95 @@ It also promises to be immutable after first read.
 
 ## Usage
 
+### Load config from file
+
+We support writing your config in php files
+
+Example: 
 ```php
+<?php
+
+// config.ph
+
+return [
+	'config-key' => 'value',
+	'nested' => [
+		'key' => 'nested-value'
+		'bool-key' => false,
+	],
+];
+```
 
-$config = new \Stefna\Config\FileConfig('path-to-php-config.php');
+```php
+$config = new \Stefna\Config\FileConfig('path-to-php/config.php');
 // config file is not read until it's needed
 
-$config->getBool('boolKey');
+$config->getBool('nested.bool-key') === false;
+$config->getString('config-key') === 'value';
 ```
 
+### Load multiple files into config
+
+```php
+<?php
+
+// common.ph
+
+return [
+	'config-key' => 'value',
+	'nested' => [
+		'key' => 'nested-value'
+		'bool-key' => false,
+	],
+];
+```
+```php
+<?php
+
+// production.ph
+
+return [
+	'config-key' => 'production-value',
+	'nested' => [
+		'extra-key' => 42,
+	],
+];
+```
+
+```php
+$config = new \Stefna\Config\FileCollectionConfig('path-to-php/');
+$config->addFile('common.php');
+$config->addFile('production.php');
+
+// config files is not read until it's needed
+
+$config->getInt('nested.extra-key') === 42;
+$config->getString('config-key') === 'product-value';
+```
+
+### Mutable config
+
+We do provide a mutable config that allows you to override values in the "root" config
+this is meant to be used when testing applications but still allow the "root" configuration to stay immutable
+
+
+```php
+$rootConfig = new \Stefna\Config\FileCollectionConfig('path-to-php/');
+$rootConfig->addFile('common.php');
+$rootConfig->addFile('production.php');
+
+$config = new \Stefna\Config\MutableConfig($rootConfig);
+
+$config->setConfigValue('config-key', 'overridden-value');
+
+$config->getString('config-key') === 'overridden-value';
+
+$config->resetConfigValue('config-key');
+
+$config->getString('config-key') === 'production-value';
+```
+
+
 ## Contribute
 
 We are always happy to receive bug/security reports and bug/security fixes