readme: update

go/utils/README.md

@@ -14,6 +14,14 @@ Package fees includes helpers for dealing with fees on Optimistic Ethereum
 
 Encodes `tx.gasLimit` based on the variables that are used to determine it.
 
+`data` - Calldata of the transaction being sent. This data should *not* include the full signed RLP transaction.
+
+`l1GasPrice` - gas price on L1 in wei
+
+`l2GasLimit` - amount of gas provided for execution in L2. Notably, accounts are charged for execution based on this gasLimit, even if the gasUsed ends up being less.
+
+`l2GasPrice` - gas price on L2 in wei
+
 #### `DecodeL2GasLimit(gasLimit *big.Int) *big.Int`
 
 Accepts the return value of `eth_estimateGas` and decodes the L2 gas limit that