Summary:
This is a documentation-only change: currently the docs imply that nested text formatting only works on iOS (via `NSAttributedString`). But the code (and my tests!) indicate it also works fine on Android via `SpannableString`, so clarify this in the documentation for the `Text` component.
Closes https://github.com/facebook/react-native/pull/7215
Differential Revision: D3223732
fb-gh-sync-id: 4e796e493ba6c48f05b812a12761ddb3851e06e1
fbshipit-source-id: 4e796e493ba6c48f05b812a12761ddb3851e06e1