Document inactive block behaviour (#447)

mesecons_detector/doc/objectdetector/description.html

@@ -2,3 +2,4 @@ The object detector is a receptor. It changes its state when a player approaches
 Right-click it to set a name to scan for.
 You can also search for comma-separated lists of players where the detector gets activated if any of the names in the list are found.
 It can also receive digiline signals which are the name to scan for on the specified channel in the right-click menu.
+Automatic scanning with Mesecons output only works when the detector is in an active block, but Digilines queries always work.