In actual fact it's not as simple as it may seem, especially if you are setting up your IDE for the first time (as I was just today). I mucked around for ages looking for the line numbers option until I found the solution elsewhere on the net. There's a bit of an unsuspecting trap for the unwary.
Under Tools/Options make sure you select the checkbox "Show all settings" in the bottom left hand corner of the Options dialogue box, now you will see under Text Editor/All Languages/General/Display the checkbox for Line numbers. It was there all the time, but I didn't see it.
btw. Is there an option for showing a thin vertical line connecting open/close braces?
Cheers.