Installation instructions don't explicitly state using Terminal

I sent my coworker, Camus, the link for [Installing Python on OSX](http://docs.python-guide.org/en/latest/starting/install/osx/), but it was not obvious to Camus that the instructions for installing `brew`:

    To install Homebrew, simply run
    $ ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

were meant to be run in `Terminal`. I grant that the entire Python Guide might be intended for more experienced developers and that new users could just go to Python.org and download the installer. I would prefer sharing the opinionated guide with a new developer, though, and not have to supplement it with digressions about what the prompt character, `$`, implies, but is not a part of the command that we paste into Terminal.

The link for `install Homebrew` in this guide is somewhat stale, but if you follow it through to the [Homebrew homepage](http://brew.sh/#install), the instructions there are a bit closer to what Camus would need (mentions Terminal, doesn't include the prompt character).
We've had this discussion many times in this project and I expect you're not familiar with them, but universal convention is to have a `$` or `#` at the beginning of a line executed in a terminal (the former indicates a regular user's prompt and the latter root's prompt). The `$` belongs here and this change will not be accepted unless you add it back.

There is a mixed audience for the Guide. For the most part though (as you can probably see from the verbiage preceding this) we expect some level of familiarity with the command-line.

I could wax poetic here about how docbook allows us to specify the `$` as a prompt and prevents users from copying it and pasting it by accident, but there's absolutely no point in me doing so because we aren't using docbook and we are not going to switch just for this.