[docs] [issue34051] Update multiprocessing example

[Windson Yang]

Windson Yang <wiwindson at gmail.com> added the comment:

Hello, @Antoine Pitrou. Maybe there is another way to let the reader know "only one process prints to standard output at a time" instead of sleep() function?

----------

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34051>
_______________________________________