add section calling out withdrawal network must be 1

Author: K-Ho

pages/builders/chain-operators/management/custom-gas-token.mdx

@@ -47,6 +47,8 @@ An OP Stack chain that uses the custom gas token feature enables an end user to
     You will NOT be able to change the address of the custom gas token after it is set during deployment.
   </Callout>
 
+  *   Additonally ensure that you have set your `baseFeeVaultWithdrawalNetwork`, `l1FeeVaultWithdrawalNetwork`, and `sequencerFeeVaultWithdrawalNetwork` to `1` so that fees can be withdrawn to L2. Also, ensure your `baseFeeVaultRecipient`, `l1FeeVaultRecipient`, and `sequencerFeeVaultRecipient` are set to the L2 address that you wish to withdraw fees to. Fee withdrawals to L1 are not currently supported, but will be added soon. For more details on these values, see the [Withdrawal Network](./configuration#withdrawal-network) section of the docs.
+
   *   Deploy the L1 contracts from `contracts-bedrock` using the following command:
 
   ```bash