Add google play demo app

Author: michal_szwarc

.gitignore

@@ -4,3 +4,4 @@
 /.idea/libraries
 .DS_Store
 /build
+/_exclude

README.md

@@ -1,7 +1,8 @@
 # MaterialSettings
 MaterialSettings - small library to create settings activity
 
-[ ![Download](https://api.bintray.com/packages/kenumir/MaterialDialogs/MaterialSettings/images/download.svg) ](https://bintray.com/kenumir/MaterialDialogs/MaterialSettings/_latestVersion)
+[![Android app on Google Play](https://developer.android.com/images/brand/en_app_rgb_wo_45.png)](https://play.google.com/store/apps/details?id=com.wt.sampleapp)
+
 
 ###Simple code:
 ```java