Add doc for CustomQualityProfilesModel

cura/Machines/Models/CustomQualityProfilesModel.py

@@ -7,6 +7,9 @@ from UM.Logger import Logger
 from cura.Machines.Models.QualityProfilesModel import QualityProfilesModel
 
 
+#
+# This model is used for the custom profile items in the profile drop down menu.
+#
 class CustomQualityProfilesModel(QualityProfilesModel):
 
     def _update(self):