add ref modifier to searchResults

technically this is more accurate as fromPromise returns promise with some fields being already observable, so there's no need to wrap the whole return value in another observable

README.md

@@ -120,7 +120,7 @@ This is useful to replace one promise based observable with another, without goi
 ```javascript
 @observer
 class SearchResults extends React.Component {
-  @observable searchResults
+  @observable.ref searchResults
 
   componentDidUpdate(nextProps) {
     if (nextProps.query !== this.props.query)