The documentary City of Ghosts begins at a black-tie gala in New York City. A group of Syrian men mingle with donors and have their pictures taken. “Maybe a little smile?” a photographer asks. But they are thinking about the struggles of their home city, where there is little smile about. They are part of “Raqqa is Being Slaughtered Silently,” a group of citizen-journalists who have documented the human-rights abuses of ISIS in the city of Raqqa, Syria.