Comedian Kevin Hart is busy these days — he has a stand-up TV series and four films in the works — yet there he was Saturday making a promo appearance for the Nike+ Run Club. Hart took a brisk 2-mile jog with one lucky runner. (Runners could use the Uber app to request a Nike+ Run Club Pacer to come run with them.) Last summer, while filming “Central Intelligence’’ in Boston, Hart went for a few impromptu 5K runs and invited fans, via Twitter, to join him.