Add explanation for BTL info deletion to README

README.md

@@ -23,12 +23,13 @@ It also provides a standalone tool if you want to use your library outside of Fr
 | Can be used with no document open                  | ![X](media/check.svg) | ![-](media/no.svg)        |
 | [CLI tool for import/export](docs/cli.md)          | ![X](media/check.svg) | ![-](media/no.svg)        |
 | Read BTL files                                     | ![X](media/check.svg) | ![X](media/check.svg)     |
-| Write BTL files                                    | ![X](media/check.svg) |  Deletes BTL extra data!  |
+| Write BTL files                                    | ![X](media/check.svg) |  Deletes BTL extra data!¹  |
 | [Import Fusion 360 tool library](docs/formats.md)  | ![X](media/check.svg) | ![-](media/no.svg)        |
 | [Import from Camotics](docs/formats.md)            | ![X](media/check.svg) | ![-](media/no.svg)        |
 | [Export to Camotics](docs/formats.md)              | ![X](media/check.svg) | ![X](media/check.svg)     |
 | [Export to LinuxCNC](docs/formats.md)              | ![X](media/check.svg) | ![X](media/check.svg)     |
 
+¹ The original FreeCAD CAM workbench tool editor deletes any unknown attributes from the tool when editing it. So if you use BTL to save BTL-only tool information like *Supplier* or *Description*, and then uninstall BTL and edit that tool with the FreeCAD tool editor again, the information will be erased.
 
 ## Screenshots