Fix README

[oxarbitrage]

As we move files and reorganize the current open pull requests, some of the demos referenced in the README may no longer work. Once things stabilize, we should review the README, fix any broken links, and update the related text where necessary to reflect the current project structure.

Resources that needs to stabilize:

• feat(rpc): Support rpc.discover endpoint ZcashFoundation/zebra#10201
• docs(openrpc): Use common crate for openrpc functionality wallet#353
• https://github.com/alchemydc/z3/compare/rpc-router...oxarbitrage:z3:openrpc-router?expand=1