* [apple] Move iOS/macOS src into common apple dir
* [apple] Enable macOS as platform in podspec
* [example] Use CocoaPods & auto-linking on macOS
* [docs] Update setup for macOS
* [package] Include apple dir in distribution
Fix cocoapods install error and warning.
```
Fetching podspec for `react-native-webview` from `../node_modules/react-native-webview`
[!] The `react-native-webview` pod failed to validate due to 1 error:
- WARN | attributes: Missing required attribute `license`.
- ERROR | version: The version of the spec should be higher than 0.
- WARN | license: Missing license type.
- WARN | source: Git sources should specify a tag.
```