[css-shapes-2] actually define outside-shape value

Author: astearns

css-shapes-2/Overview.bs

@@ -286,6 +286,14 @@ The 'shape-inside' Property</h4>
 			The shape is computed based on the content box of the element.
 		</dd>
 	</dl>
+	<dl>
+		<dt><dfn for=shape-inside>''outside-shape''</dfn></dt>
+		<dd>
+			The shape is computed based on 
+			the shape defined by the shape-outside 
+			and shape-margin properties.
+		</dd>
+	</dl>
 	<dl>
 		<dt><dfn>&lt;basic-shape&gt;</dfn></dt>
 		<dd>