[selectors-4] Update Changes list

Author: fantasai

selectors-4/Overview.bs

@@ -4069,6 +4069,8 @@ Changes since the 21 November 2018 Working Draft</h3>
 			(<a href="https://github.com/w3c/csswg-drafts/issues/2258">Issue 2258</a>)
 		<li>Added '':modal''.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/6965">Issue 6965</a>)
+		<li>Added '':fullscreen'' and '':picture-in-picture''.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/3796">Issue 3796</a>)
 		<li>Added '':seeking'', '':buffering'', and ':stalled'' media playback state pseudo-classes.
 			(<a href="https://github.com/w3c/csswg-drafts/issues/3821">Issue 3821</a>)
 		<li>Added '':muted'' and '':volume-locked'' sound state pseudo-classes.