Added note to README.md for Mac OSX .bashrc mods

When I tried to use the instructions in the readme I was getting end of line errors (because of the pt() function as oneliner), as well as seeing CLI params not being passed to the function.

$_ is not correct - it saves the parameter for the next invocation, $* is the correct parameter designator to pass all arguments as string.

see: http://tldp.org/LDP/abs/html/internalvariables.html#POSPARAMREF