Madonna has about 14 million followers on Instagram, so the American singer knows first-hand how powerful the photo-sharing social network is for “influencing.” But now she’s speaking out against Instagram and the darker side of using it. “You get caught up in comparing yourself to others,” the 60-year-old star tells The Sun in a new interview. “I think Instagram is made to make you feel bad.” She says it’s especially hard for artists to develop their art and as people…