Update README for version 2.3
Update README for version 2.3

ninjaprox/NVActivityIndicatorView,ninjaprox/NVActivityIndicatorView,bwearley/NVActivityIndicatorView,waterskier2007/NVActivityIndicatorView,waterskier2007/NVActivityIndicatorView,ninjaprox/NVActivityIndicatorView,ninjaprox/NVActivityIndicatorView,bwearley/NVActivityIndicatorView