Add documentation for 2981 implementation

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+ * `ERC2891`: add a new extension of `ERC721` to handle royalty information.([]())
  * `GovernorTimelockControl`: improve the `state()` function to have it reflect cases where a proposal has been canceled directly on the timelock. ([#2977](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2977))
  * `Math`: add a `abs(int256)` method that returns the unsigned absolute value of a signed value. ([#2984](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2984))
  * Preset contracts are now deprecated in favor of [Contracts Wizard](https://wizard.openzeppelin.com). ([#2986](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2986))

contracts/token/ERC721/extensions/draft-ERC721Royalty.sol

@@ -8,7 +8,11 @@ import "../../../utils/introspection/ERC165Storage.sol";
 import "hardhat/console.sol";
 
 /**
- * @dev TBD
+ * @dev Implementation of the ERC721 Royalty extension allowing royalty information to be stored and retrieved, as defined in
+ * https://eips.ethereum.org/EIPS/eip-2981[EIP-2981].
+ *
+ * Adds the {_setTokenRoyalty} methods to set the token royalty information, and {_setRoyalty} method to set a global
+ * royalty information.
  *
  * _Available since v4.5._
  */
@@ -21,7 +25,8 @@ abstract contract ERC721Royalty is IERC721Royalty, ERC165Storage {
     RoyaltyInfo private _royaltyInfo;
     mapping(uint256 => RoyaltyInfo) private _tokenRoyalty;
 
-    /*@dev Sets tokens royalties
+    /*
+     * @dev Sets tokens royalties
      *
      * Requirements:
      * - `tokenId` must be already mined.
@@ -39,7 +44,9 @@ abstract contract ERC721Royalty is IERC721Royalty, ERC165Storage {
         _tokenRoyalty[tokenId] = RoyaltyInfo(recipient, value);
     }
 
-    /*@dev Sets global royalty
+    /*
+     *
+     * @dev Sets global royalty
      *
      * Requirements:
      * - `recipient` cannot be the zero address.