Add supersimple tutorial

[DavidLeoni]

When Evoscratch loads, a tutorial explaining first steps should appear.

For Milestone 0.1, we can add a super simple tutorial which just shows we learnt how to do tutorials :-) It could have a couple of slides about what EvoScratch is supposed to do (don't need videos for now).

Important things to remind users:

• projects created in EvoScratch will not load in official Scratch
• to save projects you need to do File->Download to your computer / Load from your computer
• big red warn that for versions < 1.0 actual capability to reload file is NOT guaranteed, use-at-your-own-risk

[raffaelepojer]

To load a tutorial on startup https://github.com/LLK/scratch-gui/issues/3138

[DavidLeoni]

We have tutorial sample in botch-0.2, I'm closing this issue. For the real tutorial, I'll create another issue.