title: Saving a file with react Native
body: <p>I'm working on an option in my React Native app to take data from a Realm database, convert it into csv, and send it via email.
  I'm planning to use react-native-mail to send the email with the attachment.</p>
  
  <p>How can I save a text file on the user's device, so I can supply it to the native email app with react-native-mail (or for any other purpose)?</p>