DOC: fixed description of partition_backend

Author: Liudmila Mantrova

doc/src/sgml/config.sgml

@@ -7654,7 +7654,8 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir'
       </term>
       <listitem>
        <para>
-        Defines the backend to use for range partitioning. Possible values are:
+        Defines the backend to use for partitioning with declarative syntax.
+        Possible values are:
         <itemizedlist spacing="compact">
           <listitem>
             <para>