[css-inline] clarify figure 8 in response to GitHub issue 564

Author: dauwhe

css-inline/Overview.bs

@@ -772,7 +772,8 @@ Space Around Initial Letters</h3>
 	<figure>
 		<img src="images/Dropcap-J-3line-crash.png" width="480"
 		     alt="3-line drop cap with J, with descender crashing into fourth line of text">
-		<figcaption>Incorrect: three-line initial letter with descender</figcaption>
+		<figcaption>Incorrect: three-line initial letter with descender. 
+		In this font, the capital “J” extends well below the baseline (shown in red).</figcaption>
 	</figure>
 
 	Text is therefore excluded around the glyph bounding boxes of the initial letters.