React Native 运行报错 ---- SDK location not found

React Native 环境搭建完成，创建项目后，

运行报错：

    FAILURE: Build failed with an exception.
* What went wrong:
A problem occurred configuring project ':app'.
> SDK location not found. Define location with sdk.dir in the local.properties f
ile or with an ANDROID_HOME environment variable.
* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug
option to get more log output.
BUILD FAILED
Total time: 13.533 secs
Could not install the app on the device, read the error above for details.
Make sure you have an Android emulator running or a device connected and have
set up your Android development environment:

https://facebook.github.io/react-native/docs/getting-started.html