Updating readme for model-net test case

src/models/networks/model-net/README_MN_TEST.txt

@@ -4,9 +4,9 @@ will be executed in sequential mode.
 You can also run the test program manually in parallel (conservative or
 optimistic) mode as follows:
 
-mpiexec -n 4 tests/modelnet-test --sync=2 tests/modelnet-test.conf
+mpiexec -n 4 tests/modelnet-test --sync=2 (optional --nkp=n) tests/modelnet-test.conf
     <or>
-mpiexec -n 4 tests/modelnet-test --sync=3 tests/modelnet-test.conf
+mpiexec -n 4 tests/modelnet-test --sync=3 (optional --nkp=n) tests/modelnet-test.conf
 
 (1)- To run the modelnet test with the simplenet network plugin, use tests/modelnet-test.conf (default setting).
 (2)- To run the modelnet test with the torus network plugin, use tests/modelnet-test-torus.conf file.