[css-display-3] Add required status text.

Author: fantasai

css-display-3/Overview.bs

@@ -1,6 +1,7 @@
 <pre class='metadata'>
 Title: CSS Display Module Level 3
 Status: ED
+Status Text: A <a href="http://test.csswg.org/harness/results/css-display-3_dev/grouped/">preliminary implementation report</a> is available. Further tests will be added during the CR period.
 Work Status: Refining
 ED: https://drafts.csswg.org/css-display/
 Shortname: css-display