Tweak to README for OS X setup

[geoffreyanderson]

I added some really basic steps that I used to get pianobar-notify to work on OS X to the README :)

[fijimunkii]

I don't use macports, but was able to install the dependencies with

sudo cpan i /GNTP/
sudo cpan Desktop::Notify
sudo cpan common::sense
sudo cpan Getopt::Long
sudo cpan LWP::Simple
sudo cpan Pod::Usage

~~ note ~~~
after install Pod my permissions got messed up and I had to run 'Repair Permissions' in Disk Utility
make sure Growl is installed
might want to include instructions on aliasing