docs: add vacui-ui (#1338)

Author: jdegand

README.md

@@ -2009,6 +2009,7 @@ for the creation of web applications developed with Angular.
 * [ng-primitives](https://github.com/ng-primitives/ng-primitives) - A low-level UI component library with a focus on accessibility, customization, and developer experience.
 * [primitives](https://github.com/radix-ng/primitives) - Angular port of [Radix UI](https://www.radix-ui.com/) Primitives. Accessible. Customizable.
 * [ngbase](https://github.com/ng-base/ngbase) - A lightweight, flexible UI primitives library for Angular. It provides unstyled foundational Directives and components that developers can customize to match their design systems.
+* [vacui-ui](https://github.com/DanielAlcaraz/vacui-ui) - A headless Angular library of utility-first, primitives, low-level directives as foundational elements.
 
 #### UX Components