Fixed styling of available since / requirements

Co-authored-by: Frank Brückner <[email protected]>
Signed-off-by: kynx <[email protected]>

docs/book/v4/strategies/backed-enum.md

@@ -1,8 +1,10 @@
 # BackedEnum
 
-> Available since 4.8.0
+INFO: **New Feature**
+Available since version 4.8.0
 
-> Requires PHP 8.1+
+MISSING: **Installation Requirements**
+[Enumerations](https://www.php.net/manual/language.enumerations.overview.php) require PHP version 8.1 or higher.
 
 The `BackedEnumStrategy` provides **bidirectional conversion between strings 
 or integers and [Backed Enums](https://www.php.net/manual/en/language.enumerations.backed.php)**.