add step functions plugin to readme

README.md

@@ -174,6 +174,7 @@ Use these plugins to extend or overwrite the Framework's functionality...
 | **[Serverless Resources Env](https://github.com/rurri/serverless-resources-env)** <br/> After Deploy, this plugin fetches cloudformation resource identifiers and sets them on AWS lambdas, and creates local .<state>-env file | [rurri](http://github.com/rurri) | 
 | **[Serverless Run Function Plugin](https://github.com/lithin/serverless-run-function-plugin)** <br/> Run serverless function locally | [lithin](http://github.com/lithin) | 
 | **[Serverless Scriptable Plugin](https://github.com/wei-xu-myob/serverless-scriptable-plugin)** <br/> Customize Serverless behavior without writing a plugin. | [wei-xu-myob](http://github.com/wei-xu-myob) | 
+| **[Serverless Step Functions](https://github.com/horike37/serverless-step-functions)** <br/> AWS Step Functions with Serverless Framework. | [horike37](https://github.com/horike37) | 
 | **[Serverless Subscription Filter](https://github.com/blackevil245/serverless-subscription-filter)** <br/> Serverless plugin to register subscription filter for Lambda logs. Register and pipe the logs of one lambda to another to process. | [blackevil245](http://github.com/blackevil245) | 
 | **[Serverless Webpack](https://github.com/elastic-coders/serverless-webpack)** <br/> Serverless plugin to bundle your lambdas with Webpack | [elastic-coders](http://github.com/elastic-coders) | 
 | **[Serverless Wsgi](https://github.com/logandk/serverless-wsgi)** <br/> Serverless plugin to deploy WSGI applications (Flask/Django/Pyramid etc.) and bundle Python packages | [logandk](http://github.com/logandk) |