About halfway through Joe Pearlman’s “Lewis Capaldi: How I’m Feeling Now,” the Scottish pop star sets about crafting his second album. As he takes us into his songwriting process, he all but winks at the camera before walking through the ways this sort of thing tends to play out in other music documentaries: he’ll write the song, huff and puff over if it will be a hit, and we’ll suddenly fast-forward to a year later, when he’ll be playing the now-massive hit to sold-out crowds.