[css-multicol] add issue tracking links to metadata

Author: rachelandrew

css-multicol/Overview.bs

@@ -17,6 +17,8 @@ Previous Version: http://www.w3.org/1999/06/WD-css3-multicol-19990623
 Editor: Håkon Wium Lie, Opera Software, howcome@opera.com
 Editor: Florian Rivoal, On behalf of Bloomberg, https://florian.rivoal.net
 Editor: Rachel Andrew, Invited Expert, https://rachelandrew.co.uk, w3cid 81117
+Issue Tracking: Disposition of Comments https://drafts.csswg.org/css-multicol-1/issues 
+Issue Tracking: GitHub Issues https://github.com/w3c/csswg-drafts/labels/css-multicol-1
 Abstract: This specification describes multi-column layouts in CSS, a style sheet language for the web. Using functionality described in the specification, content can be flowed into multiple columns with a gap and a rule between them.
 Link Defaults: css-color (property) color, css21 (property) max-height, css-backgrounds-3 (value) hidden
 At Risk: column-gap accepting <<length-percentage>> instead of <<length>>