$S(m,q)$ is a hypergeometric function (you have take the upper limit of the sum $\infty$, as terms for $i$ bigger than $m-q$ will all vanish); a "standard" method would be to find it explicitly, and then to use a representation of it by an integral, which can be estimated by methods from asymptotic analysis. 

EDIT: I am referring to the standard technique to identify a hypergeometric series explained in e.g. Chapter 3 of the book ["A=B" by Petkovsek, Wilf, and Zeilberger][1].

Using it you will be able to write 
$$
S(m,q)=\left(\frac{\binom{m}{q}}{q+1}\right)^2\cdot _3F_0(-m,q-m,q-m;-;-1).
$$  


  [1]: http://www.math.upenn.edu/~wilf/AeqB.html