Update README.md

Change the default launch_screen.xml to keep the ratio on Android

Author: ishigamii

README.md

@@ -167,11 +167,11 @@ Create a file called `launch_screen.xml` in `app/src/main/res/layout` (create th
 
 ```xml
 <?xml version="1.0" encoding="utf-8"?>
-<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:orientation="vertical" android:layout_width="match_parent"
-    android:layout_height="match_parent"
-    android:background="@drawable/launch_screen">
-</LinearLayout>
+    android:layout_height="match_parent">
+    <ImageView android:layout_width="match_parent" android:layout_height="match_parent" android:src="@drawable/launch_screen" android:scaleType="centerCrop" />
+</RelativeLayout>
 ```
 
 Customize your launch screen by creating a `launch_screen.png`-file and placing it in an appropriate `drawable`-folder. Android automatically scales drawable, so you do not necessarily need to provide images for all phone densities.