Write a short description for each contributor's role

Now that we have the possible ways of contributing to Tails ordered by roles and skills, we should find a short sentence to describe each of this roles in an encouraging way.

For inspiration see Fedora: https://fedoraproject.org/en/join-fedora

Blueprint: https://tails.boum.org/blueprint/contribute

Parent Task: #6165 (closed)

Original created by @sajolida on 6359 (Redmine)