Upgrade React Native guides

The first stage of the "free content" strategy is now published. I added three articles to the website with detailed guides on how to upgrade React Native. This is a topic which lots of developers need help with, and feeds in quite nicely to the topic of the main course (understanding the native side of React Native).

https://reactnative.thenativebits.com/courses/upgrade-react-native/

These articles were shared via Twitter and got a good response. I also managed to get a Tweet out from the React Native Community Twitter account, which really helped to drive some traffic.