Add a section quick start at the end of the first chapter

[GaelVaroquaux]

Doing the full numpy and matplotlib chapters may be overkill for someone who wants to get a quick understanding of the basic before looking at a chapter like sympy, statistics, or scikit-learn.

The way I tackle this is usually with a super brief introduction to the basic: https://github.com/GaelVaroquaux/sklearn_ensae_course/blob/master/rendered_notebooks/01_data_manipulation.ipynb
I suggest to add the above notebook as a last section to the introduction chapter (the first one), skipping the scipy sparse stuff, and the 3D plotting part.

The various application-specific chapters, such as the sympy, statistics, or scikit-learn could than refer to this section, for people who google and land directly on them.

[aheilmaier]

@GaelVaroquaux I will give it a try. Just starting to read the CONTRIBUTING.rst. Trying to figure out to translate the requirements section for MacOSX.