Add usage note to ResendRequestChunkSize (#647)

Author: philipwhiuk

quickfixj-core/src/main/doc/usermanual/usage/configuration.html

@@ -1267,7 +1267,7 @@ <H3>QuickFIX Settings</H3>
   <TR ALIGN="left" VALIGN="middle">
     <TD> <I>ResendRequestChunkSize</I> </TD>
     <TD> Setting to limit the size of a resend request in case of missing messages.
-        This is useful when the remote FIX engine does not allow to ask for more than n message for a ResendRequest.
+        This is useful when the remote FIX engine does not allow to ask for more than n message for a ResendRequest. It also allows you to prevent a 'self-DDOS' by accidentally requesting a huge flood of messages your system isn't capable of processing if you are substantially behind for some reason.
         <P>
          E.g. if the ResendRequestChunkSize is set to 5 and a gap of 7 messages is detected,
          a first resend request will be sent for 5 messages.