Fix url to the example demo. Please, only pull after accepting this PR: https://github.com/wix/react-native/pull/2

Add demo for example app.

Mention that the GIF demo is the real Wix app and remove the old example demo until we have an updated version.

* add basic contributing guidelines to docs

* some English and formatting

* Add badges to README.md

* docs - how to run on android

* markdown formatting

* Add troubleshooting of old node

* Fix formattting

* Fix markdown and troubleshooting

relates to #1555

Usage:
    navBarCustomView: 'example.CustomTopBar', // registered component name
    navBarComponentAlignment: 'center' // 'center'/'fill'

* add v2 link to readme

* Update README.md

* Add font family support on bottom tabs

* import missing classes

* import missing class

* update document

* Support customize icon for left nav button in android

* Add navBar navBarTextFontSize support for android

* #1071 Test that Navigator forwards NavigationOptions to ViewController

* Add an argument allowing to run a single Android e2e test

* Fix style issue

* #1071 Allow changing navigation title in iOS

* Update readme to document an option for running a single test

* Update ScreenStyleDynamic.test.js

* Upgrade Gradle version

* Allow playground app to run on x86_64 emulator

* #1071 Allow changing navigation title

* #1071 Add tests for JavaScript