README.md: Add Screenshot

Author: zaoqi

README.md

@@ -15,3 +15,7 @@ $ make
 * [jailbreak](https://www.mobileread.com/forums/forumdisplay.php?f=150) and install [KUAL](https://www.mobileread.com/forums/showthread.php?t=203326)
 * install [kterm](https://github.com/bfabiszewski/kterm/releases)
 * copy `extensions` to Kindle.
+
+# Screenshot
+
+![screenshot 1](./screenshot/screenshot_2019_07_16T15_54_28+0800.png)