added contributing doc
added contributing doc

brunoziie/phonegap-plugin-localNotifications,Wizcorp/phonegap-plugin-localNotifications,Wizcorp/phonegap-plugin-localNotifications,brunoziie/phonegap-plugin-localNotifications,brunoziie/phonegap-plugin-localNotifications,brunoziie/phonegap-plugin-localNotifications,brunoziie/phonegap-plugin-localNotifications,Wizcorp/phonegap-plugin-localNotifications,Wizcorp/phonegap-plugin-localNotifications