Add Ursa.Avalonia (#163)

README.md

@@ -266,6 +266,7 @@ Contributions are always welcome! Please take a look at the [contribution guidel
 - [RangeSlider](https://github.com/DmitryNizhebovsky/Avalonia.RangeSlider) - RangeSlider control.
 - [Ripple Effect](https://github.com/Roflyanochka/AvaloniaRipple) - Sample of ripple effect.
 - [Tabalonia](https://github.com/egorozh/Tabalonia) - Tab Control with drag-able tabs.
+- [Ursa.Avalonia](https://github.com/irihitech/Ursa.Avalonia) - Ursa is a UI library for building cross-platform UIs with Avalonia UI.
 - [UVtools.AvaloniaControls](https://github.com/sn4k3/UVtools/tree/master/UVtools.AvaloniaControls) - Fast and configurable AdvancedImageBox with image modes, pan & zoom, select regions, pixel grid and cursor images
 - [Xamarin.Forms.Platform.Avalonia](https://github.com/zhongzf/Xamarin.Forms.Platform.Avalonia) - Xamarin Forms platform implemented with Avalonia (A multi-platform .NET UI framework).