doc: adjust search_path secondary index mention

per Tom Lane

doc/src/sgml/ddl.sgml

@@ -1736,7 +1736,7 @@ CREATE TABLE public.products ( ... );
 
    <indexterm>
     <primary><varname>search_path</varname></primary>
-    <secondary>run-time setting</secondary>
+    <secondary>configuration parameter</secondary>
    </indexterm>
 
    <para>