docs: add ngx-graph (#886)

Author: jdegand

README.md

@@ -941,6 +941,7 @@ become an Angular expert.
 * [unovis](https://github.com/f5/unovis) - Modular data visualization framework for React, Angular, Svelte, Vue, and vanilla TypeScript or JavaScript.
 * [angular-google-charts](https://github.com/FERNman/angular-google-charts) - A wrapper for the Google Charts library written in Angular.
 * [ngx-flexmonster](https://github.com/flexmonster/ngx-flexmonster) - A powerful and fully customizable JavaScript component for web reporting. It is packed with all core features for data analysis and can easily become a part of your Angular data visualization project.
+* [ngx-graph](https://github.com/swimlane/ngx-graph) - Graph visualization library for Angular.
 
 #### Cookies