Added USB enable-disable mode (#25)

Author: dbisu

README.md

@@ -43,6 +43,20 @@ The easiest way to so is by using a jumper wire between those pins as seen bello
 
 ![Setup mode with a jumper](images/setup-mode.png)
 
+### USB enable/disable mode
+
+If you need the pico-ducky to not show up as a USB mass storage device for stealth, follow these instructions.  
+Enter setup mode.  
+Copy boot.py to the root of the pico-ducky.  
+Copy your payload script to the pico-ducky.  
+Disconnect the pico from your host PC.
+Connect a jumper wire between pin 18 and pin 20.
+This will prevent the pico-ducky from showing up as a USB drive when plugged into the target computer.  
+Remove the jumper and reconnect to your PC to reprogram.
+The default mode is USB mass storage enabled.   
+
+![USB enable/disable mode](images/usb-boot-mode.png)
+
 ## Useful links and resources
 
 ### Docs

boot.py

@@ -0,0 +1,16 @@
+from board import *
+import digitalio
+import storage
+
+noStorageStatus = False
+noStoragePin = digitalio.DigitalInOut(GP15)
+noStoragePin.switch_to_input(pull=digitalio.Pull.UP)
+noStorageStatus = not noStoragePin.value
+
+if(noStorageStatus == True):
+    # don't show USB drive to host PC
+    storage.disable_usb_drive()
+    print("Disabling USB drive")
+else:
+    # normal boot
+    print("USB drive enabled")