add SST queue limit comment in adios2.xml

Author: pnorbert

Tutorial/heat2d/fortran/adios2.xml

@@ -17,6 +17,13 @@
         <engine type="SST"/>
         <engine type="InSituMPI"/>
 
+        SST allows for reader disconnect and reconnect. To make it useful, limit
+        the number of steps SST caches in memory with a parameter.
+            <engine type="SST">
+                <parameter key="QueueLimit" value="2"/>
+            </engine>
+
+
         DataMan is more elaborate with a transport and IP address required
         <io name="heat">
             <engine type="DataMan">