[css-grid] Add note about potentially returning used values for gCS() of grid-row-start/etc. #2681

Author: fantasai

css-grid-1/Overview.bs

@@ -1854,6 +1854,11 @@ Resolved Values</h4>
 	However, compatibility with early implementations of this module
 	requires us to define 'grid-template-rows' and 'grid-template-columns' as returning used values.
 
+	ISSUE: The CSS Working Group is considering whether to also return used values
+	for the <a>grid-placement properties</a>
+	and is looking for feedback, especially from implementors.
+	See <a href="https://github.com/w3c/csswg-drafts/issues/2681">discussion</a>.
+
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