[css-fonts-4] Update changes section for post-Sptember 2018

Author: svgeesus

css-fonts-4/Overview.bs

@@ -5083,6 +5083,10 @@ Changes
 
 <ul>
 	<li>Changed initial value of font property descriptors from normal to auto</li>
+	<li>Update syntax for font-stretch in font matching section</li>
+	<li>Update font style matching examples </li>
+	<li>Clarify description of font palettes</li>
+	<li>Stop claiming that 'ch' uses the first available font</li>
 </ul>
 
 <h3 id="changes-2018-04-10">