Document new config option

[bgravenorst]

The new configuration option tx-pool-enable-balance-check (false by default) when enabled, will make sure that pending transactions, which sender hasn't enough balance to pay their fee, cannot be in the prioritized layer, thus preventing them to occupy space there and potentially be selected for block production.

For more information, see: hyperledger/besu#9176

[m4sterbunny]

I'll take this one