contracts-bedrock: depositTransaction warning (#2678)

Addresses TOB-OPT-7:
> When a smart contract submits a deposit transaction, the code will transform the contract address to an aliased address by adding a fixed offset. Due to the lack of specification and guidance regarding how smart contracts should manage funds within the system, a naive smart contract that interacts with the DepositFeed could lock funds in the system that may not be retrievable later.

The recommendation was:
> Provide guidance within the documentation to ensure that smart contract developers are aware of this edge case.
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
Co-authored-by: Mark Tyneway <mark.tyneway@gmail.com>
Co-authored-by: Matthew Slipper <me@matthewslipper.com>

packages/contracts-bedrock/contracts/L1/OptimismPortal.sol

@@ -78,8 +78,11 @@ contract OptimismPortal is ResourceMetering {
     }
 
     /**
-     * Accepts deposits of ETH and data, and emits a TransactionDeposited event for use in deriving
-     * deposit transactions.
+     * @notice Accepts deposits of ETH and data, and emits a TransactionDeposited event for use in
+     * deriving deposit transactions. Note that if a deposit is made by a contract, its address will
+     * be aliased when retrieved using `tx.origin` or `msg.sender`. This can lead to loss of funds
+     * in some cases which the depositing contract may not have accounted for. Consider using the
+     * Bridge or CrossDomainMessenger contracts which provide additional safety assurances.
      *
      * @param _to The L2 destination address.
      * @param _value The ETH value to send in the deposit transaction.