title: react-native android fontFamily does not take effect
body: <h3>Question 1:</h3>
  <p>I add a fontFamily to index.android.js's welcome style, but it takes no effect. Does fontFamily actually work on android?</p>
  <p>welcome:{
  fontSize:20,
  fontFamily:'roboto-thin',
  textAlign:'center',
  margin:10}</p>
  <h3>Question 2:</h3>
  <p>if fontFamily works on android, is there a way to load custom font from assets? Or is this some feature to be implemented by react-native?</p>