readme: Fix wrong name namespace in dockerhub repo name
readme: Fix wrong name namespace in dockerhub repo name

Signed-off-by: Trong Nghia Nguyen <8e1f45cdcce8e4aef30b6ef5f5ba85d3ec052bb0@gmail.com>

resin-io-library/resin-rpi-raspbian,nghiant2710/resin-rpi-raspbian