[mediaqueries-4] Note lack of scan:interlace and grid:1 in the wild

Closes #1778

Author: frivoal

mediaqueries-4/Overview.bs

@@ -1307,6 +1307,8 @@ Display Type: the 'scan' feature</h3>
 		<pre>@media (scan: interlace) { body { font-family: sans-serif; } }</pre>
 	</div>
 
+	Note: At the time of writing, all known implementations match <code>scan: progressive</code> rather than <code>scan: interlace</code>.
+
 <h3 id="grid">
 Detecting Console Displays: the '@media/grid' feature</h3>
 
@@ -1341,6 +1343,7 @@ Detecting Console Displays: the '@media/grid' feature</h3>
 		</pre>
 	</div>
 
+	Note: At the time of writing, all known implementations match <code>grid: 0</code> rather than <code>grid: 1</code>.
 
 <h3 id="update">
 Display Update Frequency: the 'update' feature</h3>