added named arguments link.

Author: mumumu

language/oop5/interfaces.xml

@@ -65,7 +65,7 @@
    <warning>
     <para>
      A class that implements an interface may use a different name for its parameters than
-     the interface.  However, as of PHP 8.0 the language supports named arguments, which means
+     the interface.  However, as of PHP 8.0 the language supports <link linkend="functions.named-arguments">named arguments</link>, which means
      callers may rely on the parameter name in the interface.  For that reason, it is strongly
      recommended that developers use the same parameter names as the interface being implemented.
     </para>