[css-flexbox] fix bikeshed linking error

Author: tabatkins

css-flexbox-1/Overview.bs

@@ -47,7 +47,9 @@ spec: css-sizing-3;
 			text: max-content
 			text: fit-content
 	type: property; text: box-sizing
-spec: css-align-3; type: value; text: start
+spec: css-align-3;
+	type: value; text: start
+	type:dfn; text:alignment baseline
 spec: css-position-3; type: property; text: left
 spec: css-writing-modes-3; type: dfn;
 	text: start