[css-sizing-3] Forgot to add link to issue.

Author: fantasai

css-sizing-3/Overview.bs

@@ -45,7 +45,7 @@ Introduction</h2>
 		to allow authors to assign elements the dimensions resulting from these size calculations.
 
 
-		Issue: This spec needs illustrations! See
+		Issue: This spec needs illustrations! See <a href="https://github.com/w3c/csswg-drafts/issues/1938">issue</a>.
 
 <h3 id="placement">
 Module interactions</h3>