add status to README
add status to README

relates #17

hirden/yubico-piv-tool,hirden/yubico-piv-tool,akgood/yubico-piv-tool,Yubico/yubico-piv-tool,ato/yubico-piv-tool,akgood/yubico-piv-tool,akgood/yubico-piv-tool,ato/yubico-piv-tool,Yubico/yubico-piv-tool,akgood/yubico-piv-tool,Yubico/yubico-piv-tool