docs: changes the way ACL operations are handled

[poppyseedDev]

related to pr: #454

This PR offers chaining for ACL operations, such as these two code snippets work the same.

function _approve(address owner, address spender, euint64 amount) internal virtual {
         allowances[owner][spender] = amount;
         TFHE.allowThis(amount);
         TFHE.allow(amount, owner);
         TFHE.allow(amount, spender);
     }

using TFHE for euint64;

...

function _approve(address owner, address spender, euint64 amount) internal virtual {
        allowances[owner][spender] = amount;
        amount.allowThis().allow(owner).allow(spender);
    }