“Our work here is to change people’s vision,” says Jean-Marie Barbe, with a particularly French balance of passion and nonchalance, as if the mission he’s describing is both the simplest and most important thing in the world. A leading light of the documentary association Ardèche Images, based in his rural home village of Lussas in southeast France, he knows that’s harder than he makes it sound: He also knows the survival of his beloved artform depends on not talking up difficulties before others do. Leading docmaker Claire Simon has his back in “The Grocer’s Son, The Mayor, The Village and The World…,” an affectionate but clear-eyed study of Lussas’ unlikely status as a world capital of nonfiction filmmaking, and the exhaustive investment of time, money and hard-headed willpower that goes into sustaining that reputation.