Update SafeMath.sol

Author: danielweber90

SafeMath.sol

@@ -1,6 +1,20 @@
 // SPDX-License-Identifier: MIT
 pragma solidity >=0.7.0 <0.8.0;
 
+/**
+ * @dev Wrappers over Solidity's arithmetic operations with added overflow
+ * checks.
+ *
+ * Arithmetic operations in Solidity wrap on overflow. This can easily result
+ * in bugs, because programmers usually assume that an overflow raises an
+ * error, which is the standard behavior in high level programming languages.
+ * `SafeMath` restores this intuition by reverting the transaction when an
+ * operation overflows.
+ *
+ * Using this library instead of the unchecked operations eliminates an entire
+ * class of bugs, so it's recommended to use it always.
+ */
+ 
 library SafeMath {
     function safeAdd(uint a, uint b) internal pure returns (uint c) {
         c = a + b;