Added WebPush client documentation
Added WebPush client documentation

aerogear/aerogear-unifiedpush-server,secondsun/aerogear-unifiedpush-server,aerogear/aerogear-unifiedpush-server,secondsun/aerogear-unifiedpush-server,aerogear/aerogear-unifiedpush-server,secondsun/aerogear-unifiedpush-server