WIP: Document OpenMPI v4 performance issues w.r.t. MPI-IO

doc.zih.tu-dresden.de/docs/jobs_and_resources/mpi_issues.md

@@ -2,6 +2,13 @@
 
 This pages holds known issues observed with MPI and concrete MPI implementations.
 
+## OpenMPI v4.x.x - Performance Loss with MPI-IO-Backend OMPIO
+
+Workaround is to make use of the "old" IO-backend:
+```console
+export OMPI_MCA_io=^ompio
+```
+
 ## Mpirun on partition `alpha`and `ml`
 
 Using `mpirun` on partitions `alpha` and `ml` leads to wrong resource distribution when more than