Add issue asking for example.

Author: tabatkins

css-grid/Overview.bs

@@ -3042,6 +3042,8 @@ Aligning the Grid: the 'justify-content' and 'align-content' properties</h3>
 	(''justify-content/space-around'', ''justify-content/space-between'', ''justify-content/space-evenly'')
 	or to be resized (''stretch'').
 
+	Issue: Add example of fixed size spanner getting extra space from content-distribution.
+
 <h3 id='grid-baselines'>
 Grid Baselines</h3>