Quickstart Should Use Local Dev, Not Docker

The main quickstart uses `docker build` and `docker run`.

That takes awhile to run and isn't a great local dev experience.

Instead we should have the quickstart show the quickest way to run a function locally, like this:

```
dart run bin/server.dart
```

This is what other FF READMEs do too.

We can add the docker commands in a different section if we really want. Or reserve it to the docker doc.