Update README.md

GYSELAX/testcase_xlarge/README.md

@@ -13,5 +13,5 @@ Case2 on 384 nodes:
  - 8 MPI tasks per node
  - 1.64 Go per MPI task
 
-The number of MPI tasks per node can be changed. To do this, you need to change the number of thread.  
-If the number of thread decreases, the number of MPI tasks per node increases. The number of MPI tasks and the number of nodes is directly computed in your subgys from the number of threads. Please, read the section **Add a new machine** in ../README.md. 
+The number of OpenMP threads can be set depending on your machine. 
+Please, read the section **Add a new machine** it the application [README](../README.md).