[css-sizing-3] Link to issue tracking compressible elements & max-width/height (#6348).

Author: tabatkins

css-sizing-3/Overview.bs

@@ -1309,6 +1309,8 @@ Compressible Replaced Elements</h4>
 
 	* <{select}>, <{textarea}>, <{progress}>, <{meter}>.
 
+	Issue(6348): Tracking web-compat & implementation progress of applying this to max-width/height in <a href="https://github.com/w3c/csswg-drafts/issues/6348">Issue 6348</a>.
+
 <h2 class=no-num id="changes">
 Changes</h2>