[css-shadow-parts-1][editorial] Added Changes section

Author: SebastianZ

css-shadow-parts-1/Overview.bs

@@ -471,4 +471,16 @@ Security Considerations</h2>
 
 As [=shadow trees=] are intentionally not a security boundary,
 merely a convenience for page authors,
-exposing them to selectors in this way introduces no new security considerations.
+exposing them to selectors in this way introduces no new security considerations.
+
+<h2 id=changes>
+Changes</h2>
+
+Changes since the <a href="https://www.w3.org/TR/2018/WD-css-shadow-parts-1-20181115/">
+First Public Working Draft</a> of 15 November 2018
+
+* Add support for multiple names in ''::part()''
+* Renamed 'part name map' to [=forwarded part name list=]
+* Restructured 'part element list' algorithm
+* Moved various ''::part()'' details to [=fully styleable pseudo-element=]
+* Minor editorial improvements