Update README.md

Author: Hexeption

README.md

@@ -5,13 +5,15 @@
 ### :warning: WARNING :warning::  You **CANNOT** publish any code generated by this tool.
 
 ### Supported versions:
-1.13->1.20.2
+1.13->1.21.4
 
 ### Important
 1.17< Needs JDK 16
 
 1.18> Needs JDK 17
 
+1.21> Needs JDK 21
+
 ### How to use
 
 1. Import the build.gradle in Intellij.