[css-sizing-3] Add another previous version.

Author: tabatkins

css-sizing-3/Overview.bs

@@ -9,6 +9,7 @@ ED: https://drafts.csswg.org/css-sizing-3/
 TR: https://www.w3.org/TR/css-sizing-3/
 Editor: Tab Atkins, Google, http://xanthir.com/contact/, w3cid 42199
 Editor: Elika J. Etemad / fantasai, Invited Expert, http://fantasai.inkedblade.net/contact, w3cid 35400
+Previous version: https://www.w3.org/TR/2019/WD-css-sizing-3-20190522/
 Previous version: https://www.w3.org/TR/2018/WD-css-sizing-3-20180304/
 Previous version: https://www.w3.org/TR/2017/WD-css-sizing-3-20170207/
 Abstract: This module extends the CSS sizing properties with keywords that represent content-based "intrinsic" sizes and context-based "extrinsic" sizes, allowing CSS to more easily describe boxes that fit their content or fit into a particular layout context.