Update README.md

README.md

+# parallel-file-io kernel
+
 This POP WP7 CoDesign code implements serial ASCII file I/O, where all file I/O is undertaken by process 0, and data for file I/O operations is communicated between process 0 and other processes via point to point blocking
 sends and receives. 
 
@@ -5,12 +7,16 @@ The resulting executable takes one argument, which defines the number of double
 
 The program reports the time for process 0 to write and read all data to file, one entry per line, including the time taken to receive/send data with other processes via MPI point to point communications.
 
+## Building the code
+
 The file mpi_io_kernel.cpp should be compiled with an MPI C++ compiler with the -std=c++11 flag, e.g. 
 
 `mpicxx mpi_io_kernel.cpp -std=c++11 -o mpi_io_kernel`
 
-* kernel name: parallel-file-io
-* version:     serial-ascii
-* pattern:     serial-ascii-file-io
+## Executing the code
+
+To run the code using mpirun use the following command, replacing `nproc` with the number of processess, and `nval` with the number of double precision values per process.
+
+`mpirun -np nproc mpi_io_kernel nval`