[DOC] Define Contributor onboarding 'Cheat Sheet'

[aibcmars]

Is your feature request related to a problem? Please describe. The Contributing guide and all docs needed to read for 'perfect' contribution is quite overwhelming Let's create a 'Cheat Sheet' to simplify the onboarding.

Describe the solution you'd like Cheat sheet

• [x] define content
• [x] choose the tool to build it (image or … https://github.com/artf/grapesjs, https://www.canva.com/design/play?category=tACZCgZgEaE&type=TACRsbXUzY8) /!\ the tool should permit easy and quick edition

Additional context final output can look like this: