Add a section at the beginning with a link to this project, explaining how to contribute and improve the documentation

[teolemon]

Who for

• Developers
• Potential API doc contributors

What

• Add a section at the beginning of the published documentation with a link to this project, explaining how to contribute and improve the documentation
• Specifically, a link to https://github.com/openfoodfacts/api-documentation/issues/23

Why

• Creating a positive feedback and contribution loop

[soma2000-lang]

@teolemon I am an Gsod aspirant Can I work on this issue??