Merge pull request #366 from elukewalker/demo-link

Author: MasterKale

content/docs/tools-libraries/test-sites.md

@@ -25,5 +25,6 @@ toc: true
 - [aka.ms/webauthntest](https://aka.ms/webauthntest)
 - [lbuchs/WebAuthn](https://webauthn.lubu.ch/_test/client.html)
 - [WebAuthn Response Debugger](https://debugger.simplewebauthn.dev/)
+- [Yubico WebAuthn Developers Demo Site](https://demo.yubico.com/webauthn-developers)
 
 The ["Awesome WebAuthn"](https://github.com/herrjemand/awesome-webauthn) GitHub repo is also regularly updated with tools and demos from the community.