Add example screenshot

README.md

@@ -5,3 +5,5 @@
 A small X11-plus-Cairo statusbar for XMonad-like setups, inspired
 loosely by [xmobar](https://xmobar.org/). Heavily tailed to my own
 uses. Still terribly buggy.
+
+![an example screenshot of knurling in action](examples/screenshot-01.png)