mac stuff. also, better pip instructions

added stuff for Mac.
Also, split Pip section out into it's own thing. Pip should be
installed before virtualenv. Mac OS X, installing homebrew to install
python means that Pip is installed before you even start THINKING about
installing virtualenv. The pip installation directions are unclear, so
I went digging into the
[history](https://pypi.python.org/pypi/setuptools/1.1.6#id104).

Originally, on the first day, after light and dark, God made python
setuptools; setuptools came with easy_install, which was a much easier
way to install python packages, and all was good. However, sin came
into the world and setuptools because old and not-quite-maintained.
Thus, Distribute came along, still with easy_install to install stuff.
Then from the tree of good and evil, came a better package manager in
the form of Pip.

So for a long time, installing distribute>pip was the best way to
install packages, as http://stackoverflow.com/a/5590714 shows. However,
distribute grew mature, and there came a time where the people who made
saw fit to merge it with the old setuptools, creating the new
setuptools. Pip followed suit, and from
https://github.com/pypa/pip/commit/0e342bc1297a4fde6d622d0f152161f3cbae9
162 we can see that it recommends new setuptools >=0.8.

Thus, the current best way to install the newest stuff is to $ wget
https://bitbucket.org/pypa/setuptools/raw/bootstrap/ez_setup.py | sudo
python && wget
https://raw.github.com/pypa/pip/master/contrib/get-pip.py | sudo
python. Aka install setuptools followed by pip.

Or perhaps, just $ sudo apt-get install python-setuptools python-pip

tl;dr pip comes before virtualenv, and figured out the proper way to install pip