docs/library/pyb.rst: Update pyb.usb_mode() to mention VCP+MSC+HID.
@@ -271,6 +271,7 @@ Miscellaneous functions
- ``'MSC'``: enable with MSC (mass storage device class) interface
- ``'VCP+MSC'``: enable with VCP and MSC
- ``'VCP+HID'``: enable with VCP and HID (human interface device)
+ - ``'VCP+MSC+HID'``: enabled with VCP, MSC and HID (only available on PYBD boards)
For backwards compatibility, ``'CDC'`` is understood to mean
``'VCP'`` (and similarly for ``'CDC+MSC'`` and ``'CDC+HID'``).
