Documentation errors

I found some inaccuracies in the docs (using `1.0.0-alpha14`).

`import {metadata} from './my-document.md'` didn't work for me, instead it was `import {meta} from './my-document.md'`.

Also, using the following config threw an error:

```
directives: {
TwitterFeed: {
render: {
name: 'TwitterFeed',
source: './module/with/directives'
}
}
},
```

But this one seemed to work better:

```
{
directives: {
Thing: {
component: {
source: './components/Thing.js'
}
}
}
}
```