Update README.md

Author: cheton

README.md

@@ -2,3 +2,13 @@
 [![NPM](https://nodei.co/npm/infinite-tree.png?downloads=true&stars=true)](https://nodei.co/npm/infinite-tree/)
 
 A browser-ready tree library that can efficiently display a large tree with smooth scrolling.
+
+<i>
+**The project is under heavy development and a lot of things are changing.**<br>
+**Stay tuned for more information later.**
+</i>
+
+## Installation
+```bash
+npm install --save infinite-tree
+```