Add 'Android SDK Platform 23' to check list

Summary:
Add 'Android SDK Platform 23' to the check list when install the proper Android SDK.

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Closes https://github.com/facebook/react-native/pull/11744

Differential Revision: D4464520

Pulled By: hramos

fbshipit-source-id: 2cfabdadc8a94f35cbbd37d9dce46375e8b954c3

docs/GettingStarted.md

@@ -205,6 +205,7 @@ Android Studio installs the most recent Android SDK by default. React Native, ho
 Select "SDK Platforms" from within the SDK Manager, then check the box next to "Show Package Details". Look for and expand the `Android 6.0 (Marshmallow)` entry, then make sure the following items are all checked:
 
 - `Google APIs`
+- `Android SDK Platform 23`
 - `Intel x86 Atom System Image`
 - `Intel x86 Atom_64 System Image`
 - `Google APIs Intel x86 Atom_64 System Image`