title: adding Overlay to a MapView in osmdroid
body: <p>I am writing a simple android application using osmdroid that work online an offline untill now I am able to display the map (online and offline), and I want to add overlay (markers) on the map, I had search for simple example for using overlay in osmdroid and I tried some of them but they didn't work, so I want any example for adding overlay or marcker using osmdroid</p>