To have it work automatically could be very annoying!
It could import (by synchronize) every image in your computer. How would you keep control?
You can right-click on the top level folder of your photo hierarchy, and select Synchronize folder, and it will synchronize that folder and all child folders.
But, as warned above by wobertc, I don't know if you really want to do this. Synchronize not only imports all photos in the selected folders into Lightroom (including perhaps photos you don't want?), but it deletes from Lightroom the photos that are no longer in the folder.
A better strategy, in my opinion, is to put the photos into folders by capture date, import them (so you will do this once and never need to import or synchronize that folder again), and thus you avoid the above mentioned problems.
Thank you both. I will have to research this furthter
Thanks dj, well explained.