Insert a "Getting started" chapter after the intro"

[steinbeck]

First of all: Great Book! The structure is a bit over-systematic or academic. I suggest following the practical approach of the rdkit book and pick the people up where they usually stand, i.e. wanting to read some structures from file and do something with it. So, after the introduction and before getting into the "atom=news atom()" stuff, insert a getting-started section. See https://www.rdkit.org/docs/GettingStartedInPython.html

[egonw]

The book had a chapter like this. I did not port that yet, but will give that priority now then.

[egonw]

Ported a good bit of the original chapter now: https://egonw.github.io/cdkbook/writingApps.html