Update todo-app README.md (microsoft#7061)

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# Pull Request

## 📖 Description

A simple fix for out-date todo-list example readme.md


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## 📑 Test Plan

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## ✅ Checklist

### General

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- [ ] I have included a change request file using `$ npm run change`
- [ ] I have added tests for my changes.
- [ ] I have tested my changes.
- [ ] I have updated the project documentation to reflect my changes.
- [ ] I have read the [CONTRIBUTING](https://github.com/microsoft/fast/blob/master/CONTRIBUTING.md) documentation and followed the [standards](https://github.com/microsoft/fast/blob/master/CODE_OF_CONDUCT.md#our-standards) for this project.

## ⏭ Next Steps

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examples/todo-app/README.md

@@ -2,4 +2,4 @@
 
 A Todo app, written entirely with fast-element.
 
-> Note: A step by step tutorial will be coming to the site soon. In the mean time, you can run `npm install` and then `npm run dev` to see the example.
+> Note: A step by step tutorial will be coming to the site soon. In the mean time, you can run `npm install` and then `npm start` to see the example.