Define mq-boolean with CSS value definition syntax

Author: cdoublev

mediaqueries-4/Overview.bs

@@ -1310,6 +1310,10 @@ Detecting Console Displays: the '@media/grid' feature</h3>
 	Type: discrete
 	</pre>
 
+	<pre>
+	<dfn>&lt;mq-boolean></dfn> = <<integer [0,1]>>
+	</pre>
+
 	The '@media/grid' media feature is used to query whether the output device is grid or bitmap.
 	If the output device is grid-based
 	(e.g., a “tty” terminal, or a phone display with only one fixed font),