Add deprecation notice to README

Author: yrezgui

README.md

@@ -1,3 +1,8 @@
+> **Warning**
+> This sample has been deprecated and is no longer being maintained.
+> 
+> To find other samples that may be of interest, see [https://developer.android.com/samples](https://developer.android.com/samples).
+
 # Storage Samples Repository
 
 This repository contains a set of individual Android Studio projects to help you learn about