[css-speech-1] Note editorial changes

Author: fantasai

css-speech-1/Overview.bs

@@ -1836,3 +1836,6 @@ Appendix E &mdash; Changes</h2>
 	<li>Made the ''speak/auto'' value of 'speak' respond to 'visibility'.
 	See <a href="https://github.com/w3c/csswg-drafts/issues/511">Issue 511</a>.
 	</ul>
+
+	In addition there have been some minor editorial fixes.
+	and the source has been converted to <a href="https://speced.github.io/bikeshed/">Bikeshed</a> format.