doc: Improve tableoid description

Mention that it's useful for determining table names for partitioned
tables as well as for those in inheritance hierarchies.

Author: Ian Lawrence Barwick <barwick@gmail.com>
Reviewed-by: Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>
Discussion: https://www.postgresql.org/message-id/flat/CAB8KJ=gFmBXP=P9htziOj+WM5PDAK4qc7iGQta+8kUh306kQnw@mail.gmail.com

Author: petere

doc/src/sgml/ddl.sgml

@@ -1144,7 +1144,8 @@ CREATE TABLE circles (
 
      <para>
       The OID of the table containing this row.  This column is
-      particularly handy for queries that select from inheritance
+      particularly handy for queries that select from partitioned
+      tables (see <xref linkend="ddl-partitioning"/>) or inheritance
       hierarchies (see <xref linkend="ddl-inherit"/>), since without it,
       it's difficult to tell which individual table a row came from.  The
       <structfield>tableoid</structfield> can be joined against the