Doc clarification for synchronous_commit.

Fujii Masao

doc/src/sgml/config.sgml

@@ -1662,6 +1662,9 @@ SET ENABLE_SEQSCAN TO OFF;
         to allow the transaction to commit asynchronously.  However, the
         special value <literal>local</> is available for transactions that
         wish to wait for local flush to disk, but not synchronous replication.
+        If <varname>synchronous_standby_names</> is not set, <literal>on</>,
+        <literal>remote_write</> and <literal>local</> provide the same
+        synchronization level; transaction commit only waits for local flush.
        </para>
        <para>
         This parameter can be changed at any time; the behavior for any