[css-align] Actually specify how 'normal' aligns grid items. Fixes w3c#1433.

Author: tabatkins

css-align/Overview.bs

@@ -1175,9 +1175,10 @@ Inline/Main-Axis Alignment: the 'justify-self' property</h3>
 		<tr>
 			<th>''justify-self/normal'' Behavior
 			<td>
-				Behaves as ''justify-self/stretch'' for non-replaced items.
-				For replaced items,
+				Effectively ''justify-self/stretch'' for items with no intrinsic aspect ratio,
+				and ''justify-self/start'' for items with an intrinsic aspect ratio:
 				see <a href="https://www.w3.org/TR/css-grid-1/#grid-item-sizing">Grid Item Sizing</a> in [[!CSS-GRID-1]].
+				The resulting box is start-aligned.
 	</table>
 
     See [[!CSS-GRID-1]] for details.