Add example for applied field simulations in dielectric profile calculation how-to

We have a nice tutorial for planar dielectric profiles computed from equilibrium fluctuations. When writing our review paper I just realized that we should have another one, or at least an example script in the repository, showing how to do the same from non-equilibrium simulations. In that case, one also needs the parallel polarisation density, which is not accessible in the current interface if I am correct (using the virtual cutting)? The perpendicular can be obtained from integrating the charge profile...