This is the first substantial demo of using
the Kotlin version of Astronomy Engine from
a Java program.
Structured the README.md so I can keep adding more and
more demos as separate Java class files.
The `demotest` script builds the code and will run
each demo one at a time, verifying each one's output.
Adopted from https://stackoverflow.com/a/63332420
So one can run the demo with `./gradlew jar && java -jar build/libs/astronomy-demo-0.0.1.jar`
instead `./gradlew run`
