perpendicular-flap: Add notes for visualizing CalculiX results

Author: MakisH

perpendicular-flap/README.md

@@ -51,6 +51,8 @@ in order to use OpenFOAM and FEniCS for this test case.
 
 How to visualize the simulation results depends on the selected solvers. Most of the solvers generate `vtk` files which can visualized using, e.g., ParaView.
 
+CalculiX exports results in `.frd` format, which you can visualize in CGX (`cgx flap.frd`). In the CGX window, you can click-and-hold to select different times and fields, or to animate the geometry. If you prefer to work with VTK files, you can also use tools such as [ccx2paraview](https://github.com/calculix/ccx2paraview) or a converter included in the [calculix-adapter/tools](https://github.com/precice/calculix-adapter/tree/master/tools) directory.
+
 As we defined a watchpoint on the 'Solid' participant at the flap tip (see `precice-config.xml`), we can plot it with gnuplot using the script `plot-displacement.sh.` You need to specify the directory of the selected solid participant as a command line argument, so that the script can pick-up the desired watchpoint file, e.g. `plot-displacement.sh solid-fenics`. The resulting graph shows the x displacement of the flap tip. You can modify the script to plot the force instead.