Update documentation chapters

[demeringo]

Problem

As dicussed in #51 we could update the name of several sections of documentation.

Solution

Apply the following:

1. [x] rename "FUNCTIONAL" by explanation. I like the fact that there is 0 code nor API request in this section. It's a way to explain our methodology for non developers.
2. [x] rename "HOW TO" by reference
3. [x] Create a real "HOW TO" section with real explainable use cases
4. [x] Today, "TRY IT OUT" is a more condensed documentation than a proper tutorial. We could keep "TRY IT OUT" as an executable steel cheat and create a quick tutorial to fulfill all the goals you have presented.

Also:

5. [x] group Home and Introduction as a single topic that provides links to other sections.
6. [x] Move the useffull resources to the reference section.

[demeringo]

Closed through #54