Cite External Constraints

When our code has to be a certain way due to external design constraints, be sure to cite the constraints.

For example, if we don't use this exact spelling of depositForBurn, it won't work:

/**
 * @see {@link https://github.com/circlefin/evm-cctp-contracts/blob/master/src/TokenMessenger.sol}
 * 1ddc505 Dec 2022
 */
const TokenMessenger: TokenMessengerI = {
  depositForBurn: ['uint256', 'uint32', 'bytes32', 'address'],
};

-- pos-gmp.flows.ts#L75-L81