solana: Update fee token comment to include required burn changes (#493)

solana/programs/example-native-token-transfers/src/instructions/transfer.rs

@@ -225,7 +225,9 @@ pub fn transfer_burn<'info>(
  // would be lost.
  // To support fee tokens, we would first transfer the amount, _then_ assert
  // that the resulting amount has no dust (instead of removing dust before
- // the transfer like we do now).
+ // the transfer like we do now). We would also need to burn the new amount
+ // _after_ paying fees so as to not burn more than what was transferred to
+ // the custody.
  if after != before {
  return Err(NTTError::BadAmountAfterBurn.into());
  }