Update bulk_gaas README file

examples/Bulk-GaAs-noCIF/README.md

@@ -5,6 +5,12 @@
 Ground, DOS and Band calculations of Bulk GaAs. PW with 300 eV cutoff, 2.5 kpoint per Angstrom k-point density. The important thing is that the positions are given with Atom object. To run the calculation with MPI on 4 cores please execute the following command in this folder.
 
     mpirun -np 4 gpawsolve.py -i bulk_gaas.py
+
+or
+
+    gpaw -P4 python ~/path-to-gpawtools/gpawsolve.py -- -i bulk_gaas.py
+
+Here, ~/path-to-gpawtools shows a full path your gpaw-tools folder.
 
 When you use Atoms object inside configuration file, please note that you must add