[css-color-4] White and black luminance levels for image-p3

Author: svgeesus

css-color-4/Overview.bs

@@ -1972,6 +1972,8 @@ Predefined colorspaces: ''srgb'', ''image-p3'', and ''rec2020''.</h3>
 				<tr><th>Blue chromaticity</th><td>0.150</td><td>0.060</td></tr>
 				<tr><th>White chromaticity</th><td>0.3127</td><td>0.3290</td></tr>
 				<tr><th>Transfer function</th><td rowspan="2">same as srgb</td></tr>
+				<tr><th>White luminance</th><td rowspan="2">80.0 cd/m<sup>2</sup></td></tr>
+				<tr><th>Black luminance</th><td rowspan="2">0.80 cd/m<sup>2</sup></td></tr>
 			</table>
 
 		<dt><dfn>a98rgb</dfn>