Quickstart tutorial for running dnadna on an existing dataset adressing reviewer's comment

Reviewer's comment was

2. Concerning the section Usage Overview, I find it very helpful that the commands are explained in detail. Please include a small pre-existing (simulated) toy dataset and the dataset config file in the “DNADNA Format” to enable the execution of the example commands without running the simulation (given that it is optional when the user has the data at his disposal and just wants to get familiar with the framework’s functionality).

We use this opportunity to illustrate the use of dataset-config, and to give an example of training SPIDNA

@j.guez please review the tuto for typo/clarity, see if you can reproduce all the steps easily, check the links

For reviewing, in the branch:

cd docs/
make html
firefox _build/html/index.html

quickstart2.pdf

Remarks: #Quickstart tuto should not be renamed to ensure its automatic testing. Note that tuto 2 is not passing the automatic test for now (fails the pytest after the wget). As I moved it under section Quickstart Tuto 2 it is not an issue for CI (it's not scanning this part), but we should later see how to fix the test