[v4] update the doc around balanceDelta

[ChefMist]

• it'll be flipped via this PR: https://github.com/pancakeswap/pancake-v4-core/pull/49
• Also around exactInput for CL Pool would mean amountSpecified less than 0 eg. if amountSpecified = -100, it means swap exactly 100 tokenIn for x tokenOut

https://developer.pancakeswap.finance/contracts/v4/overview/accounting-layer-vault#reconciling-balance