现在在REMIX编译发布合约，都提示要求spdx license, 弄了半天也没搞明白怎么弄，我拷贝来的合约代码进行修改后始终无法编译，提示

xxx.sol: Warning: SPDX license identifier not provided in source file. Before publishing, consider adding a comment containing "SPDX-License-Identifier: <SPDX-License>" to each source file. Use "SPDX-License-Identifier: UNLICENSED" for non-open-source code. Please see https://spdx.org for more information.

按照这个警告提示加上了comment也编译和部署不了 恳请指导！