Documentation: List of supported Backends and its ID for Cross-chain functionalitites #427
Description
Location
README.md
Problem
Currently the go-perun's users do not have a comprehensive way to look for supported Backend and its backendIDs. This is an inconvenience for further extensions as we extend our current backends with cross-chain functionalities and implement new backend for future chains.
Proposal
Provide a section in README, that specifies the current cross-chain-supported backends with their corresponding BackendIDs. This could also includes Backends that are currently in development that will be supported in the future.