FEM: writer base, add some comment for elemnt faces constraints

src/Mod/Fem/femsolver/writerbase.py

@@ -339,6 +339,13 @@ class FemInputWriter():
             # FreeCAD.Console.PrintLog("{}\n".format(femobj["ContactSlaveFaces"]))
             # FreeCAD.Console.PrintLog("{}\n".format(femobj["ContactMasterFaces"]))
 
+    # information in the regard of element faces constraints
+    # forum post: https://forum.freecadweb.org/viewtopic.php?f=18&t=42783&p=370286#p366723
+    # contact: master and slave could be the same face: rubber of a damper
+    # tie: master and slave have to be separate faces AFA UR_ K
+    # section print: only the element faces of solid elements
+    #                from one side of the geometric face are needed
+
     def get_constraints_tie_faces(self):
         if not self.femnodes_mesh:
             self.femnodes_mesh = self.femmesh.Nodes