Quite surprised it didn't come with them!
If you want to add them as POIs, go to one of the on-line libraries of POI files
and look for a truck-stops file.
I know
PocketGPSWorld has them, look under "Food and drink" for "Truck stop cafe"
(but you may want to add some of the other categories such as "diners"?)
There's also "Truck laybys" under "Transport" which might be of interest.
To install them on the TomTom you need the "My TomTom" software on your PC.
So first, you need to download MyTomTom from the TT website here:
https://tomtom.com/en_gb/mytomtom/getstarted/
Once it's installed and running, you need to hook up the TomTom to the pc via USB,
then click on the icon in the PC's system tray
(next to the clock) and select "Add community content"
From there, you will get a browser screen (yes, it uses your web browser...) that looks something like this:
Click on the "Add POI" box and you need to add the .ov2 data files that you downloaded form the site AND the .bmp picture files that came with them, so you get the correct little icons on the TT screen.