Add comment that describes difference between this SIPO and others

[taylor-bsg]

https://github.com/bespoke-silicon-group/basejump_stl/blob/63a7c42a5611162ceab11c91fa80d52db2d3259c/bsg_dataflow/bsg_serial_in_parallel_out_dynamic.v#L3

I think the difference is that this SIPO allows the sender to determine the number of words that should be dequed together?

[dpetrisko]

https://github.com/bespoke-silicon-group/basejump_stl/blob/master/bsg_dataflow/bsg_serial_in_parallel_out.v

• sender sends fixed number of flits
• receiver notified on any received
• reciever dequeues variable number of flits https://github.com/bespoke-silicon-group/basejump_stl/blob/master/bsg_dataflow/bsg_serial_in_parallel_out_full.v
• sender sends fixed number of flits
• receiver notified on all flits received
• receiver dequeues all flits at once https://github.com/bespoke-silicon-group/basejump_stl/blob/master/bsg_dataflow/bsg_serial_in_parallel_out_dynamic.v
• sender sends variable number of flits
• receiver notified on flits == sender variable
• receiver dequeues all flits at once https://github.com/bespoke-silicon-group/basejump_stl/blob/master/bsg_dataflow/bsg_serial_in_parallel_out_passthrough.v
• same as bsg_serial_in_parallel_out_full but with zero latency