add docs

Author: frangio

contracts/utils/Arrays.sol

@@ -103,12 +103,22 @@ library Arrays {
         return slot.getUint256Slot();
     }
 
+    /**
+     * @dev Access an array in an "unsafe" way. Skips solidity "index-out-of-range" check.
+     *
+     * WARNING: Only use if you are certain `pos` is lower than the array length.
+     */
     function unsafeMemoryAccess(uint256[] memory arr, uint256 pos) internal pure returns (uint256 res) {
         assembly {
             res := mload(add(add(arr, 0x20), mul(pos, 0x20)))
         }
     }
 
+    /**
+     * @dev Access an array in an "unsafe" way. Skips solidity "index-out-of-range" check.
+     *
+     * WARNING: Only use if you are certain `pos` is lower than the array length.
+     */
     function unsafeMemoryAccess(address[] memory arr, uint256 pos) internal pure returns (address res) {
         assembly {
             res := mload(add(add(arr, 0x20), mul(pos, 0x20)))