FEM: add some comments to material and calculix solver object

src/Mod/Fem/femsolver/calculix/solver.py

@@ -317,3 +317,16 @@ def add_attributes(obj, ccx_prefs):
     )
     dimout = ccx_prefs.GetBool("BeamShellOutput", False)
     obj.BeamShellResultOutput3D = dimout
+
+
+"""
+Should there be some equation object for Calculix too.
+
+Necessarily yes! The properties GeometricalNonlinearity,
+MaterialNonlinearity, ThermoMechSteadyState might be moved
+to the appropriate equation.
+
+Furthermore the material Category should not be used in writer.
+See common materila object for more information. The equation
+should used instead to get this information needed in writer.
+"""