[css-text-decor] Clarify interaction of text-decoration with display: contents.

Author: fantasai

css-text-decor/Overview.bs

@@ -170,14 +170,19 @@ Line Decoration: Underline, Overline, and Strike-Through</h2>
     blocks.</p>
   </div>
 
+  Note: Line decorations are propagated through the box tree,
+  not through inheritance,
+  and thus have no effect on descendants
+  when specified on an element with ''display: contents''.
+
 <h3 id="text-decoration-line-property">
 Text Decoration Lines: the 'text-decoration-line' property</h3>
 
   <pre class="propdef">
   Name: text-decoration-line
   Value: none | [ underline || overline || line-through || blink ]
   Initial: none
-  Inherited: no (but see prose)
+  Inherited: no (but see prose, above)
   </pre>
 
   <p>Specifies what line decorations, if any, are added to the element.