typo in the readme

[icylace]

In the synopsis section in the readme, you have the following:

/*
 * `sum` function takes either two numbers or two strings as a parameter,
 * and returns a number or a string respectively.
 */
var add = typify("sum :: a : number|string => a -> a -> a", function (a, b) {
    return a + b;
});

It looks like var add should instead be var sum.