Autocomplete: include webauthn token example

[WilcoFiers]

This token was added to HTML 5 a while back: https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#attr-fe-autocomplete-webauthn Since the rule lists out what things are allowed I figured I'd add an explicit example for it.

Need for Call for Review: 1 week

---

How to Review And Approve

• Go to the “Files changed” tab
• Here you will have the option to leave comments on different lines.
• Once the review is completed, find the “Review changes” button in the top right, select “Approve” (if you are really confident in the rule) or "Request changes" and click “Submit review”.
• Make sure to also review the proposed Call for Review period. In case of disagreement, the longer period wins.