Adding a pip requirements file

Simplifying the script installation by adding a requirements.txt
file which can be used by pip to fulfill the script's dependencies
Updating the installation instructions

Updating the installation instructions to be more clear and to aid the
user in the proper configuration of the script
Reflowing the README file

Updating the structure of the README file to be more readable, plus
adding some links
Suggesting the use of virtualenv
Merge pull request #2 from rudisimo/requirements-update

Requirements update