docs(elements): add ng-add docs to elements guide (#23350)

PR Close #23350

aio/content/guide/elements.md

@@ -109,12 +109,14 @@ The recently-developed [custom elements](https://developer.mozilla.org/en-US/doc
 <tr>
   <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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   </td>
 </tr>
 </table>
-  
 
+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).