Add Uno Platform (#2622)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>

readme.md

@@ -205,6 +205,7 @@
 - [Low Code](https://github.com/zenitysec/awesome-low-code#readme) - Allowing business professionals to address their needs on their own with little to no coding skills.
 - [Capacitor](https://github.com/riderx/awesome-capacitor#readme) - Cross-platform open source runtime for building Web Native apps.
 - [ArcGIS Developer](https://github.com/Esri/awesome-arcgis-developer#readme) - Mapping and location analysis platform for developers.
+- [Uno Platform](https://github.com/MartinZikmund/awesome-uno-platform#readme) - Open-source .NET UI platform for building cross-platform apps.
 
 ## Programming Languages