docs/library: Update pyb.Timer to add missing args and defaults to init.
@@ -62,7 +62,7 @@ Constructors
Methods
-------
-.. method:: Timer.init(\*, freq, prescaler, period)
+.. method:: Timer.init(\*, freq, prescaler, period, mode=Timer.UP, div=1, callback=None, deadtime=0)
Initialise the timer. Initialisation must be either by frequency (in Hz)
or by prescaler and period::
