New article: Introduction to Shadow DOM

Post an introductory article along with [DevBytes video](https://www.youtube.com/watch?v=Is4FZxKGqqk).
Put HTML into one block and JS into another one.

```html
<div id="host"></div>
```

```js
var host = document.querySelector('#host');
var root = host.createShadowRoot(); // Create a Shadow Root
var div = document.createElement('div');
div.textContent = 'This is Shadow DOM';
root.appendChild(div); // Append elements to the Shadow Root 
```