Add link to the demo of Nullboard

README.md

@@ -1371,7 +1371,7 @@ See https://staticsitegenerators.net and https://www.staticgen.com
 - [Crepido](https://github.com/arshad/crepido) - Create (kanban) boards to track users and projects from flat markdown files. `MIT` `Nodejs`
 - [Kanboard](http://kanboard.net/) - Simple and open source visual task board. ([Source Code](https://github.com/kanboard/kanboard)) `MIT` `PHP`
 - [myTinyTodo](http://www.mytinytodo.net/) - Simple way to manage your todo list in AJAX style. Uses PHP, jQuery, SQLite/MySQL. GTD compliant. ([Demo](http://www.mytinytodo.net/demo/), [Source Code](https://bitbucket.org/maxpozdeev/mytinytodo)) `GPL-2.0` `PHP`
-- [Nullboard](https://github.com/apankrat/nullboard) - Single-page minimalist kanban board; compact, highly readable and quick to use. `BSD-2-Clause` `Javascript`
+- [Nullboard](https://github.com/apankrat/nullboard) - Single-page minimalist kanban board; compact, highly readable and quick to use. ([Demo](https://nullboard.io/preview)) `BSD-2-Clause` `Javascript`
 - [PHP Task/Todo list](https://github.com/lgg/tasks.php) - Simple task/todo list that uses a JSON text file for the tasks. `MIT` `PHP`
 - [Restyaboard](http://restya.com/board/) - Open source Trello-like kanban board. ([Demo](http://restya.com/board/demo.html), [Source Code](https://github.com/RestyaPlatform/board)) `OSL-3.0` `PHP`
 - [TaskBoard](http://taskboard.matthewross.me/) - Kanban-inspired app for keeping track of things that need to get done. ([Demo](https://taskboard.matthewross.me/demo.html), [Source Code](https://github.com/kiswa/TaskBoard)) `MIT` `PHP`