Adding SLURM binding policy change to README

Signed-off-by: Geoffrey Paulsen <gpaulsen@us.ibm.com>

README

@@ -2045,6 +2045,9 @@ srun:
 
    shell$ srun -N 2 hello_world_oshmem
 
+  NOTE: Starting with Open MPI v4.0.5, libmpi will honor SLURM's binding
+        policy even if that would leave the processes unbound.
+
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 The Modular Component Architecture (MCA)