Add section to README.BwAuthorities with pip/peep instructions.

need to be running the master branch from tor git.

4. Download SQLAlchemy 0.7.x-latest and Elixir 0.7.x-latest

4. Install Dependencies

4.1. Dependencies from your distribution's package manager

In Debian-based systems, the following packages are required:

    $ sudo apt-get install python2.6 libpython2.6-dev libsqlite3-dev

If you want to use postgres support, you should also install python-psycopg2.

4.2. Python Dependencies

4.2.1. Using Pip or Peep:

First, ensure that you've got a *recent* version of pip.  If you already have

pip, do:

    $ pip install --upgrade pip

Next, if you'd like to verify the correctness of the downloaded dependencies

with SHA-256 (rather than MD5, which is pip's default), do:

    $ pip install peep

Finally, do:

    $ peep install -r .../NetworkScanners/BwAuthority/requirements.txt

(Or, if you didn't install peep, do `$ pip install -r requirements.txt`.)

4.2.2. The Tedious Way

The latest version of SQLAlchemy is 0.7.2 and the latest version of Elixir

is 0.7.1 at the time of writing. While TorFlow is written to be compatible

Both these libraries also depend upon python-pysqlite2, which should be 

a package for your distribution (you want 2.3.x for SQLite 3.x).

If you want to use postgres support, you should also install python-psycopg2.

5. Enable voting on bandwidths in your authority torrc