Walkthrough for `cross-chain-swap` is Outdated

[amessbee]

There is a walkthrough of Example Swap Contact in docs here: https://docs.agoric.com/guides/orchestration/getting-started/contract-walkthrough/cross-chain-swap.html

However, Swap Contract is a work in progress at this time, and the above documentation is outdated.

Similar, the class diagram and the relevant information on the landing page is also outdated.

[mujahidkay]

Let's use this as a source of truth for progress instead. I would also argue that we remove the examples README in favor of this