Document function chaining on website

FuncUnit adds all actions to a queue to ensure that items fire in the correct order. Not only could this be made a little clearer (it helps with the overall understanding of the tool), but it should be noted that functions can be added to the chain:

``` javascript
F("input").exists().type("hello world");
$("input").text() === "hello world"; //-> not likely, due to how FuncUnit queue works

// queue up a function to run
F(function () {
$("input").text() === "hello world"; //-> true
});
```

Start by locating the FuncUnit website documentation covering action queues and chaining. Clarify that actions run in order and document how a function can be added to the chain, using the issue's JavaScript example. Done means the explanation and example are published on the website.

Written by the indexing model from the issue text.