message: docs(ctb): Add comment regarding proxy address check
diff: @@ -136,6 +136,8 @@ contract OptimismPortal is Initializable, ResourceMetering, Semver {
  // Prevent users from creating a deposit transaction where this address is the message
  // sender on L2.
  + // In the context of the proxy delegate calling to this implementation,
  + // address(this) will return the address of the proxy.
  require(
  _tx.target != address(this),
  "OptimismPortal: you cannot send messages to the portal contract"
  