Add license identifier.

Author: MoMannn

README.md

@@ -78,6 +78,7 @@ You have created and have possession of unique glass-blown artwork (each having
 To do this, simply paste the code below into Remix and deploy the smart contract. You will "mint" a token for each new piece of artwork you want to see. Then you will "burn" that token when you surrender physical possession of the piece.
 
 ```solidity
+// SPDX-License-Identifier: MIT
 pragma solidity ^0.8.0;
 
 import "https://github.com/0xcert/ethereum-erc721/src/contracts/tokens/nf-token-metadata.sol";