Summary:
Going through the `Getting Started` tutorial with `"react-native": "0.61.5"` makes the app crash when you build it, in order to get it working you must add a `.swift` file to the project.
## Changelog
Add troubleshooting content about swift errors in React Native build
Pull Request resolved: https://github.com/facebook/flipper/pull/794
Reviewed By: passy
Differential Revision: D19852986
Pulled By: mweststrate
fbshipit-source-id: 16bc44ad573dc20b90f57777ea1c9cfca7c7c4c9