Netflix’s new documentary “Joan Didion: The Center Will Not Hold,” which was released Friday, is certainly well worth a watch for anyone who’s even mildly curious about the writer who is remembered for sharply documenting American culture throughout the 20th century. I will say, however, that the film feels more sentimental than expected. But, considering that it is produced and directed by Didion’s nephew Griffin Dunne, that might not come as of a surprise. For those who are familiar with Didion, much of what is covered throughout the film may not be all that astonishing either, but there were some bits that truly stand out, this in particular: About a third of the way through, Didion is asked to recall her reaction to witnessing a 5-year-old child tripping on LSD, a character she included in her acclaimed essay “Slouching Towards Bethlehem.” Her straightforward answer is not only shocking and unexpected but acts as a revelatory window into the type of writer and journalist that Didion is.