docs/library/pyb.Pin.rst: Update the arguments for Pin.init().

Add details for Pin.init() value and alt arguments.

docs/library/pyb.Pin.rst

@@ -98,11 +98,11 @@ Class methods
 Methods
 -------
 
-.. method:: Pin.init(mode, pull=Pin.PULL_NONE, af=-1)
+.. method:: Pin.init(mode, pull=Pin.PULL_NONE, \*, value=None, alt=-1)
 
    Initialise the pin:
 
-     - ``mode`` can be one of:
+     - *mode* can be one of:
 
         - ``Pin.IN`` - configure the pin for input;
         - ``Pin.OUT_PP`` - configure the pin for output, with push-pull control;
@@ -111,14 +111,17 @@ Methods
         - ``Pin.AF_OD`` - configure the pin for alternate function, open-drain;
         - ``Pin.ANALOG`` - configure the pin for analog.
 
-     - ``pull`` can be one of:
+     - *pull* can be one of:
 
         - ``Pin.PULL_NONE`` - no pull up or down resistors;
         - ``Pin.PULL_UP`` - enable the pull-up resistor;
         - ``Pin.PULL_DOWN`` - enable the pull-down resistor.
 
-     - when mode is ``Pin.AF_PP`` or ``Pin.AF_OD``, then af can be the index or name
-       of one of the alternate functions associated with a pin.
+     - *value* if not None will set the port output value before enabling the pin.
+
+     - *alt* can be used when mode is ``Pin.AF_PP`` or ``Pin.AF_OD`` to set the
+       index or name of one of the alternate functions associated with a pin. 
+       This arg was previously called *af* which can still be used if needed.
 
    Returns: ``None``.