Update example.config.toml for fees

For phoenixd, add fee_percent and reserve_fee_min

crates/cdk-mintd/example.config.toml

@@ -27,6 +27,9 @@ mnemonic = ""
 [ln]
 # Required ln backend `cln`, `lnd`, `strike`, `fakewallet`, 'lnbits', 'phoenixd'
 ln_backend = "cln"
+# For 'phoenixd' backend, also specify fee_percent (% fee of the ln payment that mint will put in the melt quote) and reserve_fee_min (absolute amount-higher of fee_percent or reserve_fee_min is the fee reserve). 
+# fee_percent=0.04
+# reserve_fee_min=4
 
 # [cln]
 # Required if using cln backend path to rpc