docs/library: Update pyb.SPI init method to add descr about "ti" arg.
@@ -64,6 +64,7 @@ Methods
respectively.
- ``bits`` can be 8 or 16, and is the number of bits in each transferred word.
- ``firstbit`` can be ``SPI.MSB`` or ``SPI.LSB``.
+ - ``ti`` True indicates Texas Instruments, as opposed to Motorola, signal conventions.
- ``crc`` can be None for no CRC, or a polynomial specifier.
Note that the SPI clock frequency will not always be the requested baudrate.
