Add introduction tag for v5.1 contracts (#5228)

Co-authored-by: Ernesto García <ernestognw@gmail.com>

contracts/utils/Comparators.sol

@@ -2,6 +2,11 @@
 
 pragma solidity ^0.8.20;
 
+/**
+ * @dev Provides a set of functions to compare values.
+ *
+ * _Available since v5.1._
+ */
 library Comparators {
     function lt(uint256 a, uint256 b) internal pure returns (bool) {
         return a < b;