Add reference to keyboardputstring

Author: dragetd

README.md

@@ -2,4 +2,7 @@
 Converts an ASCII string to ScanCode (IBM-style 101-, 102-, and 104-key keyboards).
 
 Outputs ScanCode for KeyDown and KeyUp.
-Useful for VirtualBox's controlvm with keyboardputscancode command. See https://www.virtualbox.org/manual/ch08.html#vboxmanage-controlvm
+
+Useful for pre 5.2 VirtualBox command 'controlvm' with 'keyboardputscancode'. See https://www.virtualbox.org/manual/ch08.html#vboxmanage-controlvm
+
+**Note:** Since VirtualBox 5.2 the subcommand 'keyboardputstring' is supported and works better than this implementation!