editorial: add repo URL

Author: tantek

css-scrollbars-1/Overview.bs

@@ -6,6 +6,7 @@ Level: 1
 Status: ED
 Work Status: Revising
 ED: https://drafts.csswg.org/css-scrollbars/
+Repository: https://github.com/w3c/csswg-drafts/tree/master/css-scrollbars-1
 Editor: Tantek Çelik, Mozilla https://www.mozilla.org/, http://tantek.com/contact, w3cid 1464
 Editor: Rossen Atanassov, Microsoft, ratan@microsoft.com, w3cid 49885
 Abstract: CSS Scrollbars standardizes the ability to color scrollbars introduced in 2000 by Windows IE 5.5.