add screenshot

README.md

@@ -8,6 +8,10 @@ My solution to [https://jvns.ca/blog/2019/11/25/challenge--make-a-bouncy-window-
 Install nim and nimble and run `nimble build`. You must have XLib development headers on your system (and obviously an X server).
 
 ### How to run it?
+* Install [Xephyr](https://en.wikipedia.org/wiki/Xephyr)
+* Make sure you have a running X server
+
+Then run these commands to launch Xephyr. You could also directly execute nimwin from your `~/.xinitrc`, but that would be difficult to use.
 ```
 Xephyr -ac -screen 1280x1024 -br -reset -terminate 2> /dev/null :1 &
 env DISPLAY=:1 ./nimwin
@@ -15,3 +19,8 @@ env DISPLAY=:1 ./nimwin
 
 ### How to launch a window?
 If you want to run xterm, for example, just run `xterm -display :1`
+
+
+### Screenshots
+
+![Screenshot of htop and vim bouncing](screenshots/example.png)