[css-grid] Update Changes list.

Author: fantasai

css-grid/Overview.bs

@@ -4311,6 +4311,9 @@ Changes</h2>
 		<li>Fixed automatic sizing of grid items with an intrinsic ratio
 			so that they maintain their intrinsic ratio
 			whenever the alignment properties are ''align-self/normal'' (the default case).
+			(<a href="https://github.com/w3c/csswg-drafts/issues/523">Issue #523</a>)
+		<li>Clarified definition of <a>min-size contribution</a>.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/507">Issue #507</a>)
 	</ul>
 
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