Missing image in the Readme doc

Readme doc appears to have an image that didn't properly upload.

![echobind:fastlane-plugin-react_native_release: Simplify releases for React Native apps  2020-02-12 08-28-24](https://user-images.githubusercontent.com/7119624/74355427-ba45c800-4d71-11ea-9aa9-058821014f31.png)
