Mention fluent icons in readme

README.md

@@ -370,6 +370,7 @@ Here are some screen shots to get a feel for the UI, but things will probably ch
 ### Third party
 
 [Single Application for Qt](https://github.com/itay-grudev/SingleApplication)
+[Fluent Icons](https://github.com/microsoft/fluentui-system-icons)
 
 [Matrix]:https://matrix.org
 [Element]:https://element.io