[Docs][Android] Adds "Running on Device" note

Lots of people keep asking why they get a red screen telling them to connect to a dev server when using their device. Most have followed the "Getting Started" guide, but didn't notice the "Running on Device" section since it is kinda buried in the sidebar and isn't linked to from anywhere.

docs/GettingStarted.md

@@ -46,6 +46,8 @@ To write React Native apps for Android, you will need to install the Android SDK
 * Press the menu button (F2 by default, or ⌘-M in Genymotion) and select *Reload JS* to see your change!
 * Run `adb logcat *:S ReactNative:V ReactNativeJS:V` in a terminal to see your app's logs
 
+_Note: If you are using a device, see the [Running on Device page](http://facebook.github.io/react-native/docs/running-on-device-android.html#content)._
+
 Congratulations! You've successfully run and modified your first React Native app.
 
 _If you run into any issues getting started, see the [troubleshooting page](/react-native/docs/troubleshooting.html#content)._