How to write $\Bbb Z_q\rtimes\Bbb Z_p$ as $\langle a,b\mid a^p=b^q=1,aba^{-1}=b^{i_0}\rangle?$

Question

I am referring specifically to this example http://planetmath.org/groupsoforderpq

In Case 2, the group should be $\mathbb{Z}_q\rtimes\mathbb{Z}_p$.

How do we write it in the presentation of $$G=\langle a,b\mid a^{p}=b^{q}=1,aba^{-1}=b^{i_{0}}\rangle?$$

Thanks for help.

I am thinking of something in the directions of internal semidirect product, but not sure exactly how.