docs: mpirun --version to get MPI version (#2915)

The output of `mpirun -h` does not contain the MPI version.

doc/troubleshooting/howtoset_num_nodes.md

@@ -16,7 +16,7 @@ Set the number of processes with:
 ```bash
 mpirun -np $num_nodes dp
 ```
-Note that `mpirun` here should be the same as the MPI used to build software. For example, one can use `mpirun -h` and `lmp -h` to see if `mpirun` and LAMMPS has the same MPI version.
+Note that `mpirun` here should be the same as the MPI used to build software. For example, one can use `mpirun --version` and `lmp -h` to see if `mpirun` and LAMMPS has the same MPI version.
 
 Sometimes, `$num_nodes` and the nodes information can be directly given by the HPC scheduler system, if the MPI used here is the same as the MPI used to build the scheduler system. Otherwise, one have to manually assign these information.