update README.md

Author: xsalefter

README.md

@@ -14,6 +14,7 @@ Convenience library to help write Kill Bill plugins.
 | 4.1.y             | 0.22.z            |
 | 4.2.y             | 0.22.z            |
 | 5.0.y             | 0.24.z            |
+| 5.1.y             | 0.24.z            |
 
 We've upgraded numerous dependencies in 4.2.x (required for Java 11 support).