[Debug] Tell that the extension is for PHP 5 only

Author: nicolas-grekas

src/Symfony/Component/Debug/Resources/ext/README.md

@@ -1,7 +1,9 @@
-Symfony Debug Extension
-=======================
+Symfony Debug Extension for PHP 5
+=================================
 
 This extension publishes several functions to help building powerful debugging tools.
+It is compatible with PHP 5.3, 5.4, 5.5 and 5.6; with ZTS and non-ZTS modes.
+It is not required thus not provided for PHP 7.
 
 symfony_zval_info()
 -------------------
@@ -122,7 +124,6 @@ array(3) {
 Usage
 -----
 
-The extension is compatible with ZTS mode, and should be supported by PHP5.3, 5.4, 5.5 and 5.6.
 To enable the extension from source, run:
 
 ```