This irresistible effort has just become this year’s top-grossing documentary, and if you haven’t seen it yet, this might be a good time to catch up before the deluge of fall films hits. Veteran director Morgan Neville has made a moving and joyous behind-the-scenes film about the world of rock ‘n’ roll backup singers. It’s a universe filled with big, bold personalities and the music they make: When you say names like Darlene Love, Merry Clayton and Lisa Fischer, you are conjuring up entire universes of sound. These women sing in a way that is transformative for us, and, it turns out, for them as well. Director Neville has made that rare endeavor that pretty much everyone is guaranteed to enjoy.