README: Clarify that models should be exported with FreeCAD and sourc…

…e preferences

README.md

@@ -6,3 +6,7 @@ These source files can be in the form of:
 
 * **Scripts** - Scripts used to parametrically generate model files
 * **Native 3D model Files** - e.g. FreeCad or Solidworks models, (etc)
+
+Please note that there will be preference for scripted and free open source program generated models due to maintenance reasons.
+
+Also, even though models produced with proprietary software are accepted, the final file export should be made in FreeCAD using StepUp.