While it is true that more has been discovered about relativity since Einstein's time, that doesn't mean there isn't value in reading Einstein. When you approach an idea which is new to you, it's good to read something written for newcomers. When Einstein wrote, everyone was a newcomer. As such, his work is remarkably approachable considering how difficult the subject is.

While now I tend to think about special relativity using Minkowski space (which I find to be the easiest mental construct for me), my 12-year-old self found all that stuff in Einstein's Relativity about trains and clocks very helpful in building intuition about relativity.