Add starter project for Chapter 13

Chapter13/Start/UnoMediaCollection/UnoMediaCollection.Mobile/Android/Assets/AboutAssets.txt

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+To add cross-platform image assets for your Uno Platform app, use the Assets folder
+in the shared project instead. Assets in this folder are Android-only assets.
+
+Any raw assets you want to be deployed with your application can be placed in
+this directory (and child directories) and given a Build Action of "AndroidAsset".
+
+These files will be deployed with you package and will be accessible using Android's
+AssetManager, like this:
+
+public class ReadAsset : Activity
+{
+	protected override void OnCreate (Bundle bundle)
+	{
+		base.OnCreate (bundle);
+
+		InputStream input = Assets.Open ("my_asset.txt");
+	}
+}
+
+Additionally, some Android functions will automatically load asset files:
+
+Typeface tf = Typeface.CreateFromAsset (Context.Assets, "fonts/samplefont.ttf");