more explicit for OpenMP

Author: cphyc

src/best-practices.rst

@@ -1223,10 +1223,9 @@ OpenMP
 
 `OpenMP <http://www.openmp.org/>`_ should be compatible with
 non-openMP compilers. This can be enforced by prepending all
-OpenMP-specific calls by `!$`. Regular compilers will consider these
+OpenMP-specific calls by ``!$``. Regular compilers will consider these
 lines as comments and ignore them. For OpenMP compilers, these lines
-will be considered as regular Fortran code
-For example ::
+will be considered as regular Fortran code. The following code ::
 
     program test_openmpi
        !$ use omp_lib
@@ -1241,6 +1240,7 @@ For example ::
        print*, "nthreads=", nthreads
     end program
 
+will print the number of threads used when compiled with OpenMP. It will print by default -1 if compiled without OpenMP.
 
 MPI
 ~~~