Document existing issue

Author: dontcallmedom

issues/cookiestore-missingtask.md

@@ -1,6 +1,6 @@
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 Title: Missing tasks in parallel steps in Cookie Store API Standard
-Tracked: N/A
+Tracked: https://github.com/whatwg/cookiestore/issues/239
 Repo: 'https://github.com/whatwg/cookiestore'
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