Clarify Java 8 on 20.x versions

Author: dondonz

versioned_docs/version-v20/getting-started.mdx

@@ -10,7 +10,7 @@ import TabItem from '@theme/TabItem';
 
 # Getting started
 
-`graphql-java` requires at least Java 8.
+`graphql-java` v20.x requires at least Java 8.
 
 ## How to use the latest release with Gradle