[mediaqueries-5] Add prefers-reduced-transparency to issue about fingerprinting

Author: lukewarlow

mediaqueries-5/Overview.bs

@@ -157,7 +157,7 @@ Prefers-* Media Features Security and Privacy</h3>
 	User agents and developers implementing this
 	specification need to be aware of this vector and take it
 	into consideration when deciding whether to use the feature.
-	Specifically `prefers-reduced-motion`, `prefers-color-scheme` and
+	Specifically `prefers-reduced-motion`, `prefers-color-scheme`, `prefers-reduced-transparency` and
 	`prefers-reduced-data` are currently of concern for exploitation.
 	</div>