[w3c/webauthn] 4bb24b: Link "extension identifier" as requested in #602

  Branch: refs/heads/master
  Home:   https://github.com/w3c/webauthn
  Commit: 4bb24bfe5ddfd676eafd408efb32f9078ec4733a
      https://github.com/w3c/webauthn/commit/4bb24bfe5ddfd676eafd408efb32f9078ec4733a
  Author: Jeffrey Yasskin <jyasskin@chromium.org>
  Date:   2017-10-12 (Thu, 12 Oct 2017)

  Changed paths:
    M index.bs

  Log Message:
  -----------
  Link "extension identifier" as requested in #602

https://github.com/w3c/webauthn/pull/602#discussion_r144167932