Wrong way to start watchify in readme

[roosmaa]

In the README the assets? task definition is a bit wrong.

    p.Task("assets?", nil,  func(c *do.Context) {
        // The "?" tells Godo to run this task ONLY ONCE regardless of
        // how many tasks depend on it. In this case watchify watches
        // on its own.
	    c.Run("watchify public/js/index.js d -o dist/js/app.bundle.js")
    }).Src("public/**/*.{css,js,html}")

It should use c.Start(..) instead of regular run, otherwise this task would never finish as the watchify process will only exit when killed.