Update unl field description of xrp-ledger.toml

[tequdev]

https://xrpl.org/docs/references/xrp-ledger-toml#validators

An HTTPS URL where one can find the list of other validators this validator trusts. If the validator is configured to use a validator list site for UNL recommendations, this MUST match the server's configuration. For the production XRP Ledger network, use https://vl.ripple.com (trailing slash optional).

Add https://vl.xrplf.org in addition to https://vl.ripple.com.