Add documentation and code samples for DID Resolver on XRPL

[zshahzadpumacy]

This update adds documentation for the XRPL DID Resolver, explaining how to use, and verify DIDs on the XRP Ledger. It walks through fetching a DID from the ledger, retrieving and processing the DID document, and verifying signatures. The guide assumes a DID already exists on XRPL and also includes a snippet for generating a signature if needed. This should help developers easily integrate the resolver into their projects."