add info abot usage of strftime(3), see #1823

svn path=/icecast/trunk/icecast/; revision=18802

doc/icecast2_config_file.html

@@ -478,6 +478,7 @@ An optional value which will set the maximum number of listeners that can be att
 <h4>dump-file</h4>
 <div class="indentedbox">
 An optional value which will set the filename which will be a dump of the stream coming through on this mountpoint.
+This filename is processed with strftime(3). This allows to use variables like %F.
 </div>
 <h4>intro</h4>
 <div class="indentedbox">