[css-text-decor-4] Make underline aligned outward rather than centered on position, per WG feedback.

Author: fantasai

css-text-decor-4/Overview.bs

@@ -219,7 +219,8 @@ Text Underline Offset: the 'text-underline-offset' property</h3>
 	</table>
 
 	<ul>
-		<li>The line is centered on the specified position.
+		<li>The line is aligned to the outside of the specified position.
+		    (Below for ''under''/''auto'' positions, above for ''over''.)
 		<li>Positive lengths represent inward distances; negative lengths outward.
 		<li>Automatic adjustments made to accommodate descendant content are maintained;
 			the 'text-underline-offset' is in addition to those.