Fix extension registration example in README.md

README.md

@@ -30,7 +30,7 @@ Additionally, you need to make your registration file known in your **ext_localc
 
 ```PHP
 // register mail templates
-$GLOBALS['sg_mail']['my_extension_key']['unique_template_name'] = \TYPO3\CMS\Core\Utility\ExtensionManagementUtility::extPath('my_extension_key') . '/Configuration/SgMail/MyTemplate.php';
+$GLOBALS['sg_mail']['my_extension_key']['unique_template_name'] = 'EXT:my_extension_key/Configuration/SgMail/MyTemplate.php';
 ```
 
 sg_mail will automatically parse valid configuration files of all extensions within your TYPO3 instance.