[css-scroll-anchoring-1][editorial] Add changes section.

Author: tabatkins

css-scroll-anchoring-1/Overview.bs

@@ -324,3 +324,12 @@ Privacy and Security Considerations</h2>
 This specification,
 as it only adjusts how we compute scroll positions,
 introduces no new privacy or security considerations.
+
+<h2 id='changes' class="no-num">
+Changes</h2>
+
+<h3 id='changes-20200211'>
+Changes Since the Feb 11 2020 Working Draft</h3>
+
+	* Added definitions of [=viable candidate=] and [=priority candidate=].
+	* Clarified interaction between scroll anchoring and [=scroll snapping=].