Document role of `callValueRefundAddress` in `IInbox.sol`

[frangio]

nitro-contracts/src/bridge/IInbox.sol

Line 81 in 0770fe0

* @param callValueRefundAddress l2Callvalue gets credited here on L2 if retryable txn times out or gets cancelled. In case this address is a contract, funds will be received in its alias on L2.

From elsewhere in the docs:

this is also called the beneficiary, who's got a critical permission to cancel the ticket

I believe this should be featured in IInbox.sol as well.