Modifications to demo contract

[JesseAbram]

Hey, just went through the docs, got things to work. Just some comments. In the demo contract

contract PotLike {
    function chi() external returns (uint256);
    function rho() external returns (uint256);
    function drip() external returns (uint256);
    function join(uint256) external;
    function exit(uint256) external;
    function pie(address) public view returns (uint);

}

Chi should be sent to view so I can call it later here to get the proper balance

function balance() public view returns (uint256) {
       uint256 pie = pot.pie(address(this)); 
       uint256 chi = pot.chi();
       return pie * chi / RAY;
    }

Anyways thought I would point that out cheers!

[JesseAbram]

This is linked to PR42