What luck! I'd just run down this video, SWEATER FINISHING 101-Part 3
for the Tank of Many Colors thread. She shows short rows on the sleeve but the principle is the same. I'm not having luck so far finding the shaping of an armhole video but you're smart, you know what works for the sleeve can work for the armhole. Be sure to ask about any hitches. I'm learning a lot about short rows for armholes and sleeves that I plan to use on my next sweater project.