Add a DOM manipulation with web-sys example to examples/ and the guide

[fitzgen]

General info on the DOM: https://developer.mozilla.org/en-US/docs/Web/API/Document_Object_Model

• Add an example to examples/ that shows off working with the DOM
• Add a subsection to "web-sys >> examples" in the guide that includes this example

[ibaryshnikov]

There is dom example in the guide: https://rustwasm.github.io/docs/wasm-bindgen/examples/dom.html
Does it solve this issue?

[fitzgen]

Yep! Thanks @ibaryshnikov :)