Update README.md

Author: cheton

README.md

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 [![NPM](https://nodei.co/npm/cncjs-controller.png?downloads=true&stars=true)](https://www.npmjs.com/package/cncjs-controller)
 
 **A controller library for event-based communication between client and CNCjs server**
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+This branch is for CNCjs 2.0.0 or later versions. If you're looking for the previous version (<= 1.9), please visit the [v1](https://github.com/cncjs/cncjs-controller/tree/v1) branch.
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 ## Installation
 
 ```sh