Filmmaker Waad al-Kateab spent years documenting the horror and humanity of life in Aleppo, Syria. When she fled with her family, she smuggled 12 hard drives of footage past a Syrian checkpoint. That footage became the Oscar-nominated documentary “For Sama.” Al-Kateab and her collaborator Edward Watts tell us how they crafted an intimate 90-minute film dedicated to al-Kateab’s daughter.