Better docs landing page for Superchain contributors

[ryscheng]

What is it?

Currently we only have this index page for contributors https://docs.opensource.observer/docs/contribute/

which assumes that you already know what you want to add to OSO, and you just need to be routed to the page to teach you how.

Imagine someone who is a talented data scientist that just wants to help, Jonas had some great feedback that this person probably wants:

• An overview of how OSO plugs into retro funding
• What impact you have if you contribute to OSO metrics
• A link to a project board of metrics/data we need help with
• Official avenues for support (discord, discussions, etc)