[css-2020] Add css-grid-2 to rough interop section (not quite the right place but we don't have a better one) per WG resolution. #4715

Author: fantasai

css-2020/Overview.bs

@@ -420,6 +420,12 @@ Modules with Rough Interoperability</h3>
 			In the grid layout model, the children of a grid container
 			can be positioned into arbitrary slots in a predefined flexible or fixed-size layout grid.
 
+		<dt><a href="https://www.w3.org/TR/css-grid-2/">CSS Grid Layout Module Level 2</a>
+		  [[!CSS-GRID-2]]
+		<dd>
+			Extends and supersedes [[CSS-GRID-1]],
+			introducing “subgrids” for managing nested markup in a shared grid framework.
+
 		<dt><a href="https://www.w3.org/TR/css-will-change-1/">CSS Will Change Level 1</a>
 		  [[CSS-WILL-CHANGE-1]]
 		<dd>