Describe differences between glamorous and glamorous-native

[atticoos]

The README should describe the differences between this package and the main glamorous package.

To briefly summarize:

• The built-in component factories - glamorous.div() vs glamorousNative.view()
• React Native component property and style property forwarding detection. This uses React Native's component style prop types to determine if styles are supported. There's still room for improvement outlined in https://github.com/robinpowered/glamorous-native/issues/9 and https://github.com/robinpowered/glamorous-native/issues/10
• The use of StyleSheet over glamor - this effectively accomplishes the same thing in React Native - registering a style for a given rule