[css-images-4] Update changes

Author: svgeesus

css-images-4/Overview.bs

@@ -2346,6 +2346,7 @@ Changes {#changes}
 <h3 class="no-num" id="changes-20170413">Changes Since the <a href="https://www.w3.org/TR/2017/WD-css-images-4-20170413/">13 April 2017</a> Working Draft</h3>
 
 <!-- to 3 Nov 2021 -->
+- Defined fetching of external images
 - Added &lt;color-interpolation-method> to all gradient functions
 - Added the -webkit-image-set() alias
 - Clarified the image-resolution property