Added screenshot and build instructions

README.md

@@ -1,3 +1,15 @@
 # kennson
 
 A terminal utility to pretty print JSON.
+
+![Screenshot showing kennson pretty printing a JSON file](screenshot.png)
+
+## Build instructions
+
+Make sure you have [Dart](https://dart.dev/get-dart) installed, then run the following:
+
+```bash
+dart compile exe bin/kennson.dart
+```
+
+The compiled executable will be inside the `bin` folder, named `kennson.exe` (regardless of platform).