Explain that a bit, so you don't have to cross-ref with the C module

frontend/device/input.lua

@@ -334,6 +334,9 @@ function Input.close(path)
     if fd then
         local ok, err = input.close(fd)
         if ok or err == C.ENODEV then
+            -- Either the call succeeded,
+            -- or the backend had already caught an ENODEV in waitForInput and closed the fd internally.
+            -- Regardless, that device is gone, so clear its spot in the hashmap.
             Input.opened_devices[path] = nil
         end
     else