Add syntax declaration to code block in README.md

README.md

@@ -19,6 +19,7 @@ Features
 Example
 -------
 
+```php
  // Modbus master UDP
  $modbus = new ModbusMaster("192.168.1.1", "UDP"); 
  // Read multiple registers
@@ -33,3 +34,4 @@ Example
  }
  // Print data in string format
  echo PhpType::bytes2string($recData);
+```