Enter a Project > next to the Project name, select the down arrow (down caret) > select "Export PDF Cover Pages"
Print the cover pages > place them as cover pages for each physical document > scan the cover pages + their corresponding documents as a single file into Truss. Make sure the cover page is first.
Once this is done, select your name (top-right) > "Upload Scanned PDF"
Upload the scanned PDF into Truss. And that's it!
Truss will automatically sort each document into its corresponding task for that Project.
Additionally, here's a short video showing how this is done.