add note about down load

desktop/README.md

@@ -8,6 +8,9 @@
 A short (8k) loader program. This is responsible for copying
 the rest to a RAM card (if available), then invoking the main app.
 
+NOTE: The second half may be used for "Down load", i.e. copy
+Selector entries to RAMCard as well.
+
 ## DESKTOP2.$F1
 
 This is large - 111k. It includes a loader and the DeskTop app with

desktop/sys.s

@@ -910,6 +910,9 @@ prodos_loader_blocks:
 
         .assert * = $3000, error, "Segment length mismatch"
 
+;;; SPECULATION: This copies Selector entries marked
+;;; "Down load" / "At boot" to the RAMCard as well
+
 .proc part2
         jsr     SLOT3ENTRY
         jsr     HOME