add link to test repo

README.md

@@ -6,7 +6,7 @@ This is the repository for the W3C WebAuthn Working Group, producing the draft *
 * [The editor's copy is available at https://w3c.github.io/webauthn/](https://w3c.github.io/webauthn/), or in the [`gh-pages` branch of this repository](https://github.com/w3c/webauthn/blob/gh-pages/index.html).
 * [The build history is available at Travis-CI.org](https://travis-ci.org/w3c/webauthn/builds)
 * [W3C WebAuthn Blog](https://www.w3.org/blog/webauthn/)
-
+* [Web platform tests repository](https://github.com/w3c/web-platform-tests/tree/master/webauthn)
 # Contributing
 
 Before submitting feedback, please familiarize yourself with [our current issues list](https://github.com/w3c/webauthn/issues) and review the [mailing list discussion](https://lists.w3.org/Archives/Public/public-webauthn/).