Refine CSP doc

[chengduoZH]

with fluid.while(steps=buffer_size):
  fluid.send(ch, step)
  fluid.close_channel(ch)

==>

with fluid.while(steps=buffer_size):
  fluid.send(ch, step)

fluid.close_channel(ch)

Because once the channel is closed, Send will not put data into the channel but return false.

[wangkuiyi]

Thanks @chengduoZH !