Document that postmaster.opts is excluded from base backups

Fujii Masao

doc/src/sgml/protocol.sgml

@@ -1727,6 +1727,11 @@ The commands accepted in walsender mode are:
          <filename>postmaster.pid</>
         </para>
        </listitem>
+       <listitem>
+        <para>
+         <filename>postmaster.opts</>
+        </para>
+       </listitem>
        <listitem>
         <para>
          <filename>pg_xlog</>, including subdirectories. If the backup is run