If $z_{1}$ and $z_{2}$ are two complex numbers such that $\left|z_{1}+z_{2}\right|=\left|z_{1}\right|+\left|z_{2}\right|$, then arg $\left(z_{1} \omega\right)-\arg \left(z_{2}\right.$ i), where $\omega$ is the complex cube root of unity, is
(a) 0
(b) $\frac{\pi}{2}$
(c) $\frac{\pi}{3}$
(d) $\frac{\pi}{6}$