update to java 21

README.md

@@ -3,7 +3,7 @@
 ## Generating standings on demand
 
 - Download jar file from the [latest release](https://github.com/mrbusche/trap-scoring/releases)
-- You will need [Java 17](https://adoptium.net/) to run the jar file
+- You will need [Java 21](https://adoptium.net/) to run the jar file
 - Open command prompt to directory with downloaded jar file
 - Run `java -jar trap-5.1.2.jar` (make sure you have the correct filename from the release)
 - There will be output as the process generates the file