Update superchain explainer

[bradleycamacho]

Description

https://docs.optimism.io/get-started/superchain

Shorten signifantly and ensure we are positioning Superchain values and intent very clearly. Ping @bradleycamacho as needed for this issue as it might be a large lift

Action items

1. Do research on topic and raise any questions with the docs team
2. Write a first draft. It doesn't have to be worded perfectly as the docs team will review
3. Ping @bradleycamacho on discord and request review
4. Implement feedback from @bradleycamacho
5. Publish