[docs] Fixed arguments name when calling command decorator

There are two small types in Clock's example here.

These arguments are not correct:

@command(din_type=str, dout_type=str)

They should be:

@command(dtype_in=str, dtype_out=str)

Here is the original example: https://gitlab.com/marc2332/pytango/-/blob/develop/examples/Clock/Clock.py