showing how this formula comes from
- https://github.com/Uniswap/v2-periphery/blob/master/contracts/libraries/UniswapV2Library.sol#L43
- https://github.com/Uniswap/v2-periphery/blob/master/contracts/libraries/UniswapV2LiquidityMathLibrary.sol#L17
ua: reserveA ub: reserveB
sa: truePriceTokenA sb: truePriceTokenB