WATCH: R.A. Dickey teaches Letterman how to throw a knuckleball

CBSMets pitcher R.A. Dickey appeared on “Late Show with David Letterman” and threw his knuckleball for the late-night host. The storybook season continues for R.A. Dickey. The Mets pitcher appeared on “Late Show with David Letterman” Wednesday to discuss his late-career success – and teach the host how to…