feat: document and incentivize "good first issue"

[lucaaamaral]

feat: document and incentivize "good first issue"

Problem

There are always small issues available so a beginner could solve and learn from it. This can be used to bring in more people to learn more about the project and capacitate so they can solve more complex issues.
Beginners should be incentivized to take those issues, solve them and collaborate with the community. Magma is already complex enough.

Solution

Create a page or section under "Contribute > Community".
Bring some context in this page and invite people over to contribute, guiding on a "first steps" or "setting up a dev environment".

Non-goals

Anything specifically excluded from the concept

[lucaaamaral]

Assigned to @see7e

[see7e]

As the sidebars struture is now static (#36), is issue and related PRs should wait for it's merge.