Add more release notes.

Author: mattbertolini

RELEASE_NOTES.md

@@ -5,7 +5,10 @@ IN PROGRESS
 
 - Added preliminary support for Java records.
 - JDK 17 is now required to build this project. The production artifacts are still compiled to Java 1.8 bytecode.
+- Upgrade to Spring Framework 5.3.13
+- Upgrade to Spring Boot 2.4.13
 - Upgraded to equals verifier 3.10
+- Moved the Gradle build from Groovy DSL to Kotlin DSL
 
 ## 0.4.0
 Released 2021-06-20