beginning of dust integration page

This is just a start, but I think it might be good to get in to start review/discussion.

Still notably TODO is the docs for `{@formatMessage}`.
Actually what I wrote here probably doesn't make sense. I think we could instead end up with something more like:

```handlebars
<a href="{{npmUrl 'intl-messageformat'}}">{{code "intl-messageformat"}}</a>
```