[css-align] Add issue

Author: fantasai

css-align/Overview.bs

@@ -250,6 +250,9 @@ Positional Alignment: the ''center'', ''start'', ''end'', ''self-start'', ''self
 	<p class='issue'>
 		Add example images.
 
+	<p class='issue'>
+		Make it easier to understand the dual-axis nature of "start" and "end" wrt orthogonal flows.
+
 <h3 id='baseline'>
 Baseline Alignment: the ''baseline'' and ''last-baseline'' keywords</h3>