Need a reference/proof for computing the regularity of ideal of points in $\mathbb P^d$?

Question

In a lecture notes on 'Cohomology modules' i read the following remark:

Given a set $X$ of points in $\mathbb P^d$,using the Local Cohomology modules one can easily compute the reg$(S_X)$ where $S_X=\frac {S}{I_X}$,and $I_X$ is the homogeneous ideal of $X$.

Could anyone please explain me that how do we find reg$(S_X)$ in the mentioned case?