[w3c/webauthn] 3c8ed1: update README.md

  Branch: refs/heads/master
  Home:   https://github.com/w3c/webauthn
  Commit: 3c8ed1b942f061a5cef0bbdcd09d093c8310cf1c
      https://github.com/w3c/webauthn/commit/3c8ed1b942f061a5cef0bbdcd09d093c8310cf1c
  Author: =JeffH <Jeff.Hodges@KingsMountain.com>
  Date:   2016-12-07 (Wed, 07 Dec 2016)

  Changed paths:
    M README.md

  Log Message:
  -----------
  update README.md

add a couple more links to echidna info