Publish content about internship

Summary:
Explain what's Nasqueron and what are our values.

Describe the kind of contributions possible.

Provide a simple charte graphique.

Ref T1880.

Test Plan: Proofread, ensure navigation is easy

Reviewers: dereckson

Maniphest Tasks: T1880

Differential Revision: https://devcentral.nasqueron.org/D3119