link to other tutorials

howto/yubikey.md

@@ -81,3 +81,10 @@ protocol for non-TPO hosts, you may add this at the end of `~./ssh/config`:
     Host *
       IdentityAgent /dev/null
       IdentityFile ~/.ssh/id_ed25519_sk
+
+# Reference
+
+## Other documentation
+
+ * [Anarcat's old (2015) Yubikey howto](https://anarc.at/blog/2015-12-14-yubikey-howto/)
+ * [Yubikey cheatsheet](https://debugging.works/blog/yubikey-cheatsheet/)