Update Fetch Validator Status Documentation - Clarify the reference to the Trustee seed

[WadeBarnes]

Update the documentation to clarify the use of the Trustee seed when using von-network in the initial demo. The use of the Trustee seed in this case is simply for convenience. It is a well known seed used by von-network, and it has the privileges to fetch the extended validator info data from the nodes. In real life you would use a NETWORK_MONITOR seed/DID for this purpose.

https://github.com/hyperledger/indy-node-monitor/tree/main/fetch-validator-status#run-the-validator-info-script