doc(android): clarify documentation and types for sdkVersion field

Author: peitschie

README.md

@@ -264,15 +264,11 @@ var isSim = device.isVirtual;
 
 ## device.sdkVersion (Android only)
 
-Will return the Android device's SDK version.
+Get the Android device's SDK version ([SDK_INT](https://developer.android.com/reference/android/os/Build.VERSION#SDK_INT)).
 
 ### Supported Platforms
 
 - Android
-- Browser
-- iOS
-- Windows
-- OS X
 
 ### OS X and Browser Quirk
 

types/index.d.ts

@@ -30,6 +30,8 @@ interface Device {
     isVirtual: boolean;
     /** Get the device hardware serial number. */
     serial: string;
+    /** Get the SDK version of the Android operating system. (Android-only) */
+    sdkVersion?: string;
 }
 
 declare var device: Device;