message: docs(elements): add ng-add docs to elements guide
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diff: @@ -109,12 +109,14 @@ The recently-developed [custom elements](https://developer.mozilla.org/en-US/doc
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  <td>Edge</td>
  <td>Working on an implementation. <br>
  - Use the <a href="https://cli.angular.io/" target="_blanks">CLI</a> to automatically set up your project with the correct polyfill: <code>ng add @angular/elements</code>.
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  +In browsers that support Custom Elements natively, the specification requires developers use ES2015 classes to define Custom Elements - developers can opt-in to this by setting the `target: "es2015"` property in their project's `tsconfig.json`. As Custom Element and ES2015 support may not be available in all browsers, developers can instead choose to use a polyfill to support older browsers and ES5 code.
  +Use the [Angular CLI](https://cli.angular.io/) to automatically set up your project with the correct polyfill: `ng add @angular/elements --name=*your_project_name*`.
  - For more information about polyfills, see [polyfill documentation](https://www.webcomponents.org/polyfills).
  - For more information about Angular browser support, see [Browser Support](guide/browser-support).
  