update readme

Author: etimberg

README.md

@@ -114,9 +114,11 @@ To download a zip, go to the Chart.Annotation.js on Github
 To install via npm:
 
 ```bash
-npm install Chart.Annotation.js --save
+npm install chartjs-plugin-annotation --save
 ```
 
+Prior to v0.2.0 this plugin was known as Chart.Annotation.js. You can still install this old version via NPM.
+
 ## Documentation
 
 You can find documentation for Chart.js at [www.chartjs.org/docs](http://www.chartjs.org/docs).