Add Diagrams.net per PR #337 conversation

README.md

@@ -273,6 +273,7 @@
 
 * [DrawThe.Net](http://go.drawthe.net/) - Javascript tool that uses a YAML-formatted input to programmatically create large, complex, and visually solid diagrams.
 * [Mermaid](https://mermaid-js.github.io/mermaid-live-editor/) - Javascript module with a unique, easy, shorthand syntax. Integrates into several other tools like Grafana.
+* [Diagrams.net](https://app.diagrams.net/) - A.K.A. [Draw.io](https://app.diagrams.net/). Easy to use Diagram UI with a plethora of templates.
 
 ## Distributed Filesystems