OSError with CMSIS-DAP v2 on Windows

Hi,

I am observing the following error with CMSIS-DAP v2 (WinUSB) devices either running DAPLink ver. 0254 or Cypress KitProg3:

C:\Users\anjo>pyocd list
Exception ignored in: <function _AutoFinalizedObjectBase.del at 0x0000017F52B96E18>
Traceback (most recent call last):
File "c:\users\anjo\appdata\local\programs\python\python37\lib\site-packages\usb_objfinalizer.py", line 84, in del
self.finalize()
File "c:\users\anjo\appdata\local\programs\python\python37\lib\site-packages\usb_objfinalizer.py", line 144, in finalize
self._finalizer()
File "c:\users\anjo\appdata\local\programs\python\python37\lib\weakref.py", line 552, in call
return info.func(*info.args, **(info.kwargs or {}))
File "c:\users\anjo\appdata\local\programs\python\python37\lib\site-packages\usb_objfinalizer.py", line 104, in _do_finalize_object_ref
obj._do_finalize_object()
File "c:\users\anjo\appdata\local\programs\python\python37\lib\site-packages\usb_objfinalizer.py", line 71, in _do_finalize_object
self._finalize_object()
File "c:\users\anjo\appdata\local\programs\python\python37\lib\site-packages\usb\backend\libusb1.py", line 604, in _finalize_object
lib.libusb_unref_device(self.devid)
OSError: exception: access violation writing 0x0000000000000024

The problem appears when running any command in pyOCD, however, commands itself do work. Looks like this is known issue with pyusb/libusb:
https://github.com/pyusb/pyusb/issues/203
https://github.com/pyusb/pyusb/pull/227
https://github.com/libusb/libusb/issues/412

I can reproduce this on Windows only with Python3 + libusb 1.0.22. In order not to confuse user with this exception, I propose to update README with an recommendation to use libusb 1.0.21 under Windows until problem is fixed.

OS: Win10 Pro x64
Python: v3.7.3 x64
libusb: MinGW64 v1.0.22

Review the README's Windows installation guidance in light of the reported pyocd command error with Python 3 and libusb 1.0.22. Document the recommendation to use libusb 1.0.21 on Windows until the pyusb/libusb problem is fixed, then verify that the wording clearly covers the affected setup.