Documentation - Missing Section

[mienaikoe]

react-native link wasn't working for me because of #261, so I followed the manual installation documentation for android.

I wasn't able to get react-native run-android to work, and so I noticed that there was a step missing from the documentation that I had seen in other react-native manual installations. Specifically, adding
include ':react-native-firestack'
project(':react-native-firestack').projectDir = new File(rootProject.projectDir, '../node_modules/react-native-firestack/android')
To settings.gradle

Would be happy to send a PR. Just let me know if that's how you guys roll.