title: Add search bar to react-native-maps when using expo
body: <p>I would like to add a search bar to my maps screen and then use google to find the location associated with the input text and move the map there.</p>
  
  <p>This is what I have right now:</p>
  
  <pre><code>import React, { Component } from 'react';
  import {
      View
  } from 'react-native';
  import { Mapview } from 'expo';
  
  export default class screen extends Component {
  
      constructor(props) {
          super(props);
          this.state = {
              initialRegion: {
                  latitude: 37.78825,
                  longitude: -122.4324,
                  latitudeDelta: 0.0922,
                  longitudeDelta: 0.0421,
              }
          };
      }    
      render() {
          return (
              &lt;View&gt;
                  &lt;MapView
                      style={{ flex: 1 }}
                      initialRegion={this.state.initialRegion}
                  /&gt;
              &lt;/View&gt;
          )
      }
  }
  </code></pre>
  
  <p>I cannot find this feature in the <code>react-native-maps</code> documentation. Is this something I need to build myself?</p>