Readme should tell users to put the jar into libs/ rather than lib/

Updated readme to put GLWallpaperService.jar into libs/ rather than lib/ in new live wallpaper projects.

Prevents ClassNotFoundException from being thrown while loading the user's WallpaperService class.

https://github.com/markfguerra/GLWallpaperService/issues/28
http://stackoverflow.com/questions/10074938/android-class-path-exception

From the docs:
http://tools.android.com/recent/dealingwithdependenciesinandroidprojects