Update README.md

Author: forthommel

README.md

@@ -17,3 +17,9 @@ For instance, if a local source-build of CepGen is used, these two can take the
 export CEPGEN_LIBS_DIR=<path/to/cepgen/sources>/build
 export CEPGEN_INCLUDE_DIR=<path/to/cepgen/sources>
 ```
+
+In this example, the `dummy_process` Fortran double-precision typed function is built from the `*.f` source files (here, only [dummy_process.f](dummy_process.f), and registered using the [ProcessesWrapper.cpp](ProcessesWrapper.cpp) file.
+This latter acts as a link between the CepGen runtime environment and this new process definition.
+Two functions are respectively declaring the main matrix element, and registering it into the runtime database.
+* `DECLARE_FORTRAN_FUNCTION( dummy_process )` takes the F77 name of the function as an argument.
+* `REGISTER_FORTRAN_PROCESS( dummy, "A dummy Fortran process", dummy_process )` links this function to a new CepGen process named `dummy`, described with the second argument.