favicon

I noticed an error about `localhost:8080/favicon.ico` not being found after an initial create-choo-app, which I found odd because `create-choo-app` creates an `assets/icon.png` file. I was able to get it working with:

```bash
npm start -- --html [ --favicon assets/icon.png ]
```
Though I imagine adding that arg to the `start` script is less than ideal. Is there another way this is supposed to work?

This is obviously low priority, just wanted to list it.

Reproduce the missing localhost:8080/favicon.ico after an initial create-choo-app, then inspect the generated start script and the assets/icon.png file. Compare the default npm start behavior with the reported --favicon argument; done means a newly created app serves its favicon without requiring that manual option.

Written by the indexing model from the issue text.