[DOCS] Add new page about superchain-registry

[sbvegan]

Brief Description of the Docs Request

The superchain registry is still a wip but soon we'll be having chains making PRs.

Description of the Documentation You'd Like

Overview of the registry and point to the contributing doc in the registry repo

Links to Related Pages

New page under the Op Stack section

Additional Context

https://github.com/ethereum-optimism/superchain-registry