[w3c/webauthn] bd6264: Clarify that extensions are optional

  Branch: refs/heads/vijaybh/lots-of-fpwd-issues
  Home:   https://github.com/w3c/webauthn
  Commit: bd6264f74eb0312a1eeb9651d9cec8d2f02ac7d3
      https://github.com/w3c/webauthn/commit/bd6264f74eb0312a1eeb9651d9cec8d2f02ac7d3
  Author: Vijay Bharadwaj <vijaybh@users.noreply.github.com>
  Date:   2016-05-06 (Fri, 06 May 2016)

  Changed paths:
    M index.src.html

  Log Message:
  -----------
  Clarify that extensions are optional

Fixes #74