add whatsNew.md

Author: Rufus31415

whatsNew.md

@@ -0,0 +1,4 @@
+[![UnderAutomation Universal Robots communication SDK](https://raw.githubusercontent.com/underautomation/UniversalRobots.NET/refs/heads/main/.github/assets/banner.png)](https://underautomation.com)
+
+- fix issues related to license key activation in "Single File" applications
+- add .NET 9 support, remove .NET 7 support