Update README.md (#1756)

Add WUI (Window User Interface Library)

Author: ud84

README.md

@@ -135,6 +135,7 @@ A curated list of awesome C++ (or C) frameworks, libraries, resources, and shiny
 * [tbox](https://github.com/tboox/tbox) - A glib-like multi-platform c library. [Apache2] [website](http://tboox.org/)
 * [Ultimate++](http://www.ultimatepp.org/) - A C++ cross-platform rapid application development framework. [BSD]
 * [Windows Template Library](http://sourceforge.net/projects/wtl/) - A C++ library for developing Windows applications and UI components. [Public]
+* [WUI](https://github.com/intent-garden/wui) - WUI (Window User Interface Library) is a cross-platform library for creating graphical user interfaces in C++17+ [Boost][website](https://libwui.org)
 * [xtd](https://github.com/gammasoft71/xtd) - Modern C++20 framework to create console (CLI), forms (GUI) and unit tests (xUnit) applications on Windows, macOS, Linux, iOS, Android, FreeBSD and Haiku. [MIT]
 * [Yomm2](https://github.com/jll63/yomm2) - Fast, Orthogonal, Open multi-methods. Supersedes [Yomm11](https://github.com/jll63/yomm11) [Boost]