Update doc for mulitiple knife-rackspace gem version issue and fix.

Note, this is the first _ever_ time I have forked, pulled, requested.  Please let me know 
if I did this wrong, and sorry for any trouble.

Thanks
Boyd

+++++++

If you have older versions of the gem also installed, this causes the
"v2" functionality to be flakey.  (From IRC with Matt Ray, tested by
me)  

Included warning and command examples to show how to check and remedy 
this situtation.