added test cases README

DYNAMICO/testcase_large/README.md

+Test case presentation
+======================
+
+This case is defined as the RUN_NB640.
+
+It is small run to validate the execution. 
+This test is used to evalutate the performance of the computer. May scale up to 80000-100000 cores or up to 640GPUs. 32x32x10=10240 domains are defined. 
+
+Reference time for 10 days simulation on Jean-zay : 
+  * CPU No I/O             : 3000s on 5120 cores (128 nodes)
+  * GPU No I/O             :  782s on  160 GPUs  (40 nodes)
+
+
+        

DYNAMICO/testcase_medium/README.md

+Test case presentation
+======================
+
+This case is defined as the RUN_NB40.
+
+It is small run to validate the execution. 
+
+Reference time on Jean-zay : 
+  * CPU No I/O             : 38s on 800 cores
+  * GPU No I/O             : 80s on   4 GPUs
+
+
+       
+

DYNAMICO/testcase_medium_xios/README.md

+Test case presentation
+======================
+
+This case is defined as the RUN_NB40_XIOS.
+
+It is small run to validate the execution. Comparison can be done with or without IO servers to look at the impact on the performance.
+
+Reference time on Jean-zay : 
+  * No I/O             : 38s on 800 cores
+  * With IO server     : 57s with 800 cores for dynamico and 8 xios servers
+
+
+Running with XIOS IO servers requiered to execute run in MPMD mode, i.e. with dynamico and xios io server independant executable.
+
+Typically the running command for OpenMPI of type :
+
+mpirun -np 40 icosa_gcm.exe : -np 20 xios_server.exe
+
+IO server processes must be spread all along the node reservation. We advice one IO server by node, shared with icosa_gcm.exe executable.
+
+XIOS is not multithreaded, so the difficulty is to merge on the same node the multithreaded dynamico model. Be carefull about the binding and placement.
+       
+       
+