[TechDraw] Add context to zh_CN README file for description changes
[TechDraw] Add context to zh_CN README file for description changes

[skip-ci]
Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master,Fat-Zer/FreeCAD_sf_master