nixOS: Failed to connect to the YubiKey: connecting to pscs: the Smart card resource manager is not running#137

Per the README, I've added ``` services.yubikey-agent.enable = true; ``` to my `/etc/nixos/configuration.nix` I (successfully) rebuilt with `sudo nixos-rebuild switch` however when attempting `yubikey-agent -setup` I recieve the error ``` nixOS: Failed to connect to the YubiKey: connecting to pscs: the Smart card resource manager is not running ``` I've done some googling but have not seen anything relevant. Other apps work with the yubikey, like fido via firefox, and the YubiKey personalization tool. I've successfully used the yubikey-agent to set up keys on my Mac after installing with homebrew. Is some other set up required on nixOS that isn't documented in the README? Thanks!