If you have Pro membership (or above) you can add an "Additional File" to your models. Examples of files you can include are extra file formats for the model, high resolution or alternate textures, "readme" documentation, and tutorials on how best to use your model.
Prepare your additional file: All the files and folders must be compressed into a single ZIP, RAR, or 7z archive. The maximum total file size (after compression into an archive) is 2 GB.
Go to the Model Properties editor for the model.
Find the "Attach additional file" section
Click "Upload File", and choose the archive you prepared.
You can also delete or replace an existing additional file by clicking the three dots icon in the "Attach additional file" section.
You can view the contents of an additional file by clicking "See all files" under the "Download size" row of the model information. The additional file archive will also be available to download.