doc: Update pg_constraint.conexclop docs for WITHOUT OVERLAPS

Fixup for commit fc0438b.

Author: Paul A. Jungwirth <pj@illuminatedcomputing.com>
Discussion: https://www.postgresql.org/message-id/57ea0668-5205-426e-b934-efc89f2186c2@illuminatedcomputing.com

Author: petere

doc/src/sgml/catalogs.sgml

@@ -2806,7 +2806,8 @@ SCRAM-SHA-256$<replaceable>&lt;iteration count&gt;</replaceable>:<replaceable>&l
        (references <link linkend="catalog-pg-operator"><structname>pg_operator</structname></link>.<structfield>oid</structfield>)
       </para>
       <para>
-       If an exclusion constraint, list of the per-column exclusion operators
+       If an exclusion constraint or <literal>WITHOUT OVERLAPS</literal>
+       primary key/unique constraint, list of the per-column exclusion operators.
       </para></entry>
      </row>