documentation bug fix on mirred

documentation bug fix on mirred

Stephen,

Heres another on top of the others i sent. If you get the time, can
update your git tree with these patches?
If you are planning to make a release soon, please ping me - I have at
least one more patch that i need to work on.

cheers,
jamal

Update mirred usage to fix a bug noticed by
Andy Furniss <lists@andyfurniss.entadsl.com>
Also make it a little more readable.