[css-inline-3] Mark issue wrt bad illustration w3c#11364 w3c#10703

Also seek-oss/capsize#205 (comment)

Author: fantasai

css-inline-3/Overview.bs

@@ -1158,6 +1158,9 @@ Text Edge Metrics: the 'line-fit-edge' property</h3>
 			''line-fit-edge/cap'', and ''line-fit-edge/ex''.
 			The red lines indicate the layout bounds of the inline box.
 		</figcaption>
+
+		ISSUE(11364): This illustration doesn't match actual font metrics,
+		it's actually illustrating the cap-height, not the ascent.
 	</figure>
 
 	<div class="note">