Add contributing guide

[Gabrielle-Ribeiro]

Is your feature request related to a problem? Please describe.

The project doesn't have a contributing guide.

Describe the solution you'd like

I'd like to have a contributing guide that explains how someone can contribute with our project.

Describe alternatives you've considered

Use the contributing guide provided by Github.

Additional context

Checklist

• The issue has a meaningful name.
• The issue has a meaningful description.
• The issue has screenshots when needed.
• The issue has labels.