Riemann sum of a sine function.

Question

I have to calculate this.

$$\int_{0}^{\pi}\! \sin(x) \ dx = 2$$

And I'm able to reach this.

$$S_n=\pi\sum_{k=1}^{n}\!\frac{1}{n}\sin(\frac{k\pi}{n})$$

I'm not sure how to proceed to evaluate the sum. Any help would be great.