Updated readme to include XPF banner

readme.md

@@ -1,3 +1,5 @@
+[![GH_Banner](https://user-images.githubusercontent.com/552074/218457976-92e76834-9e22-4e35-acfa-aa50281bc0f9.png)](https://avaloniaui.net/xpf)
+
 [![Telegram](https://raw.githubusercontent.com/Patrolavia/telegram-badge/master/chat.svg)](https://t.me/Avalonia)
 [![Gitter](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/AvaloniaUI/Avalonia?utm_campaign=pr-badge&utm_content=badge&utm_medium=badge&utm_source=badge) [![Discord](https://img.shields.io/badge/discord-join%20chat-46BC99)]( https://aka.ms/dotnet-discord) [![Build Status](https://dev.azure.com/AvaloniaUI/AvaloniaUI/_apis/build/status/AvaloniaUI.Avalonia)](https://dev.azure.com/AvaloniaUI/AvaloniaUI/_build/latest?definitionId=4) [![Backers on Open Collective](https://opencollective.com/Avalonia/backers/badge.svg)](#backers) [![Sponsors on Open Collective](https://opencollective.com/Avalonia/sponsors/badge.svg)](#sponsors) ![License](https://img.shields.io/github/license/avaloniaui/avalonia.svg)
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