Put existing examples prominently in the docs

[giro090]

There are two examples from user feedback that didn't yet make their way into the new docs, the wide-to-long data processing and an end-to-end example with cleaning and extra formatting. It would be good to feature these more prominently in the docs somewhere - either at the end of the tutorial, or just linked to in the text to bring users' attention to them.

Definition of done:

• The wide-to-long data and the end-to-end example are referred to somewhere in the docs.