[CSS Parser] Added link to WICG repo

Author: gregwhitworth

css-parser-api/readme.md

@@ -2,5 +2,4 @@ CSS Parser Explainer
 ====================
 
 This specification is not currently being worked on in the Houdini TF.
-Instead, it will be worked on in a WICG repository.
-This document will link to that repository once it exists.
+Instead, it will be worked on in a [WICG repository](https://github.com/WICG/CSS-Parser-API).