Inform users when pcscd is required

Closes str4d/age-plugin-yubikey#83.

README.md

@@ -18,6 +18,15 @@ cargo install age-plugin-yubikey
 
 Help from new packagers is very welcome.
 
+### Linux, BSD, etc.
+
+On non-Windows, non-macOS systems, you need to ensure that the `pcscd` service
+is installed and running. On Debian or Ubuntu, you can do this with:
+
+```
+$ sudo apt-get install pcscd
+```
+
 ### Windows Subsystem for Linux (WSL)
 
 WSL does not currently provide native support for USB devices. However, Windows

i18n/en-US/age_plugin_yubikey.ftl

@@ -12,6 +12,7 @@
 -yubikey = YubiKey
 -yubikeys = YubiKeys
 -age-plugin-yubikey = age-plugin-yubikey
+-pcscd = pcscd
 
 ## CLI commands and flags
 
@@ -185,6 +186,22 @@ err-slot-has-no-identity = Slot {$slot} does not contain an {-age} identity or c
 err-slot-is-not-empty    = Slot {$slot} is not empty. Use {-flag-force} to overwrite the slot.
 err-timed-out            = Timed out while waiting for a {-yubikey} to be inserted.
 err-use-list-for-single  = Use {-cmd-list} to print the recipient for a single slot.
+
+err-yk-no-service-macos = The Crypto Token Kit service is not running.
+rec-yk-no-service-macos =
+    You may need to restart it. See this Stack Exchange answer for more help:
+    {"  "}{$url}
+
+err-yk-no-service-pcscd = {-pcscd} is not running.
+rec-yk-no-service-pcscd =
+    If you are on Debian or Ubuntu, you can install it with:
+    {"  "}{$apt}
+
+err-yk-no-service-win = The Smart Cards for Windows service is not running.
+rec-yk-no-service-win =
+    See this troubleshooting guide for more help:
+    {"  "}{$url}
+
 err-yk-not-found         = Please insert the {-yubikey} you want to set up
 err-yk-wrong-pin         = Invalid PIN ({$tries} tries remaining before it is blocked)
 err-yk-general           = Error while communicating with {-yubikey}: {$err}

src/error.rs

@@ -141,6 +141,35 @@ impl fmt::Debug for Error {
             Error::UseListForSingleSlot => wlnfl!(f, "err-use-list-for-single")?,
             Error::YubiKey(e) => match e {
                 yubikey::Error::NotFound => wlnfl!(f, "err-yk-not-found")?,
+                yubikey::Error::PcscError {
+                    inner: Some(pcsc::Error::NoService),
+                } => {
+                    if cfg!(windows) {
+                        wlnfl!(f, "err-yk-no-service-win")?;
+                        let url = "https://learn.microsoft.com/en-us/windows/security/identity-protection/smart-cards/smart-card-debugging-information#smart-card-service";
+                        writeln!(
+                            f,
+                            "{}",
+                            fl!(crate::LANGUAGE_LOADER, "rec-yk-no-service-win", url = url),
+                        )?;
+                    } else if cfg!(target_os = "macos") {
+                        wlnfl!(f, "err-yk-no-service-macos")?;
+                        let url = "https://apple.stackexchange.com/a/438198";
+                        writeln!(
+                            f,
+                            "{}",
+                            fl!(crate::LANGUAGE_LOADER, "rec-yk-no-service-macos", url = url),
+                        )?;
+                    } else {
+                        wlnfl!(f, "err-yk-no-service-pcscd")?;
+                        let apt = "sudo apt-get install pcscd";
+                        writeln!(
+                            f,
+                            "{}",
+                            fl!(crate::LANGUAGE_LOADER, "rec-yk-no-service-pcscd", apt = apt),
+                        )?;
+                    }
+                }
                 yubikey::Error::WrongPin { tries } => writeln!(
                     f,
                     "{}",